There are many different rune pages you can run with Maokai. This one is probably the most standard one.

The magic penetration marks can be switched out with a few different things such as attack speed or flat ability power, but it's generally better to just have this penetration.

As far as seals go, there really aren't any other optimal choices, you need the armor to survive in the jungle and you need it if you want to gank without dying in two hits.

The magic resist glyphs can be swapped out for cooldown reduction if the enemy team doesn't have a source of magic damage or you could also get scaling magic resist glyphs, but those are generally not as good on maokai as most of your ganking is done in the early levels (which I'll talk about more later!)

The movement speed quints are a must in my opinion. You need to be very active in the early/mid-game because those parts of the game are your strongest points. Having extra movement speed will help you with ganking and getting to places faster, may it be objectives, lanes or camps.

Masteries on Maokai vary depending on your playstyle. I feel like this is the most generic mastery page you can run on him and I really recommend using it.

As far as the 21 points in Offense go, you'll get the increased clearing time with butcher and will help you regenerate off killing units with feast. You also have increased cooldown reduction (very important stat on Maokai) and the utility masteries like Expose Weakness.

The 9 point in Defense are the basic jungler masteries. Increased health, reduced damage taken from neutral monsters, etc.

The Hunter's Machete with 4 health pots is the optimal start for most junglers, including Maokai. There's no reason to start with anything else as you will need the sustain from the health pots and the extra damage from the machete. You're also going to end up building your machete in to a Spirit of the Ancient Golem. Make sure you also pick up a Warding Totem and ward the opposite buff you're starting from (if you're starting blue, which I highly recommend, ward your red!)

These are a few of the best items you can get on Maokai. A big part of playing Maokai is adapting to what the enemy team has. This build is for a split magic damage and attack damage team.

If the enemy team is full ad, then you might want to avoid getting a locket and a spirit visage, instead getting a thornmail and a randuin's. It really depends on the game and who's strong.

If the enemy team had a ton of magic damage and an ad carry that is really weak, then you might consider getting a Banshee's Veil or an Abyssal Scepter. Once again, it really depends.

The build order doesn't really matter, it really depends on how the game is going. You're always going to start with the machete and the health potions, but after that it changes a lot. If you're getting kills early, then you're going to want to rush mobility boots over your Ancient Golem, if you're just farming and can't seem to get kills or anything, you definitely want to get your Ancient Golem before even considering tier 2 boots.

Mobility boots are only good to get if you're planning on snowballing, don't ever get them if you're behind, it'll be a waste of money and you seeing you don't get any tenacity from Ancient Golem anymore, you're going to be missing out on that.

As far as the rest goes, I just like getting a Kindlegem and building it in to a Spirit Visage as soon as possible, cooldown reduction is an amazing stat on Maokai at all stages of the game so make sure you prioritize that.

You usually want to start by getting sapling toss at level 1 and stacking them on the buff you're starting at (I'd recommend blue!). After that, make sure you get Arcane Smash as that will you be your main clearing ability and damage ability. Once you're level 3, get Twisted Advance so you can start ganking!

In terms of spells to max, you start by maxing your Arcane Smash then you follow up with your Twisted Advance and you finish off by maxing Sapling Toss. Make sure to get your ultimate at levels 6, 11 and 16.

Summary:

Level 1 : Sapling Toss
Level 2 : Arcane Smash
Level 3 : Twisted Advance
Level 4 : Arcane Smash
Level 5 : Arcane Smash
Level 6 : Vengeful Maelstrom
Level 7 : Arcane Smash
Level 8 : Twisted Advance
Level 9 : Arcane Smash
Level 10 : Twisted Advance
Level 11 : Vengeful Maelstrom
Level 12 : Twisted Advance
Level 13 : Twisted Advance
Level 14 : Sapling Toss
Level 15 : Sapling Toss
Level 16 : Vengeful Maelstrom
Level 17 : Sapling Toss
Level 18 : Sapling Toss

You're going to need flash on Maokai, there's no reason to get anything else. Flash is just such an overpowered summoner spell, especially when you combine it with your Twisted Advance (W). You can get some really good engages off by flash w'ing a carry and knocking them in to your team while having your ult up.

Smite is required for jungling, the objective and buff control it provides is absolutely necessary.

Sap Magic (Passive)

Each time a champion near Maokai casts a spell, he gains a charge of Magical Sap. When he has 5 charges, his next melee attack drains energy from his target, healing Maokai for 7% of his maximum health.

This passive is extremely strong, it's great for sustaining in fights and in the jungle. Make sure you keep track of your stacks and auto-attack something once it's at 5 charges to gain a huge amount of hp back (huge because you're going to have Spirit Visage!)

Arcane Smash (Q)

Maokai releases an arcane shockwave. Enemies within 100 units are knocked back and all affected enemies take magic damage and are slowed for 1.5 seconds.

MAGIC DAMAGE: 70 / 115 / 160 / 205 / 250 (+40% AP)
SLOW: 20 / 27 / 34 / 41 / 48%

The damage this spell deals is really good but the slow and the knockback are what make it amazing. It's really important to use this properly when ganking or teamfighting. You can use it to cancel ultimates that are channeled (Warwick, Katarina, Malzahar, etc.) because of the knockback. You can also use it to push enemies in to your team or just straight up slow them for 50% (which is pretty huge by the way).

Twisted Advance (W)

Maokai transforms into a cloud of arcane energy that quickly travels to a target enemy, deals magic damage and roots it. Damage is capped at 300 against minions and monsters.

MAGIC DAMAGE: 9 / 10 / 11 / 12 / 13% (+3% per 100 AP) of target's maximum health
ROOT DURATION: 1 / 1.25 / 1.5 / 1.75 / 2

This is your main form of crowd control. The root duration is pretty good, and it will allow you to setup for an Arcane Smash + Sapling Toss combo. The % health damage is pretty good as well, depending on who you use it on.

You're generally going to want to use this on carries in teamfights OR on the enemy frontline, depending on your playstyle. Either you peel for your carries by rooting the targets going on them or you dive the enemy carries and root them in hope of a follow up from your teammates.

It's also really important to note that you can dodge channeled ultimates (Karthus for example) and any other skillshot if you use your Twisted Advance when it's about to hit you. I'll have a picture/gif demonstrating what I mean in a later portion of this guide.

Sapling Toss (E)

Maokai flings a sapling that deals magic damage on impact. The sapling wards the nearby area, and will chase enemies that approach, exploding to deal magic damage and slowing enemies hit by 50% for 1 second. Saplings last for 35 seconds.

MPACT MAGIC DAMAGE: 40 / 60 / 80 / 100 / 120 (+40% AP)
EXPLOSION MAGIC DAMAGE: 80 / 120 / 160 / 200 / 240 (+60% AP)

It's really important to land this on the target you're going for as it will deal a fair amount of damage but most importantly it will slow their movement speed for 50%. Generally, you want to Twisted Advance the person, throw your sapling on them and knock them backwards with your Arcane Smash. By doing this, they should be rooted and slowed for a good amount of time, which should give your teammates time to follow up and take out the target without a problem.

Something that is overlooked about these saplings is that they last 35 seconds, that's half of your initial warding totem. Make sure you use these saplings as a form of warding! You can check bushes and even leave them in the enemy jungle to know where they are!

Vengeful Maelstrom (R)

Maokai creates a magical vortex around himself, protecting him and allied champions by reducing damage from non-turret sources by 20% for a maximum of 10 seconds.

When the effect ends the absorbed energy is released, dealing magic damage to enemies within the vortex's range, plus bonus magic damage based on the damage stored by the damage reduction effect.

MAGIC DAMAGE: 100 / 150 / 200 (+50% AP) (+2 per damage absorbed)
MAX STORED DAMAGE: 200 / 250 / 300
MAX TOTAL DAMAGE: 300 / 400 / 500 (+50% AP)

The fact that Maokai's Ultimate follows him around is absolutely absurd and overpowered. He receives 20% less damage taken while it's toggled and can also detonate it to deal a good amount of damage (especially at lower levels!) You're going to want to keep this on for as long as you're teamfighting. Try to soak as much damage as possible while having it enabled and make sure you detonate it while people are within range of the vortex, to get the most efficiency of it.

Ganking is a really important aspect of the game when you're playing Maokai. Farming won't make you a monster and you really need to have good presence early game and mid game as you really fall off late game, especially if you're not ahead. That being said, I usually go for a gank on mid/top at level 3, depending on what champions I have on my team.

It's also good to keep in mind that even if the lanes are pushed to the enemy tower, it doesn't mean you can't gank. If those lanes really are pushed to the enemy tower, guess who's getting ganked? Chances are that your lane will get ganked, you can set up and wait in a bush to countergank, they will be surprised and won't expect you to be there so you'll be at an advantage.

The best way to get good with ganking/counterganking is to have wards up in the enemy jungle, you'll be able to know where they're going to and just knowing what part of the jungle they're in is a huge advantage for you and your team, it will give your teammates the chance to be more aggressive if they know he's in the top part of the jungle and they're in the bottom side. Good wards to place in the enemy jungle are usually around their blue buff and at their wraith camp.

I usually start at Blue Buff when playing Maokai, I'll get a point in my Sapling toss and throw down saplings where the blue buff spawns starting 1:20. I'll throw down as many as I can before it hits 1:55. The reason I do this is because saplings last 35 seconds before they blow up, so if you start throwing them at 1:20, the first one will blow up right as the blue buff spawns and you'll get more damage on to the buff.

Once you've gotten the buff, you want to clear a small camp (wraiths or wolves) then go for your red. After completing your red, look for a gank as soon as possible. You have the best level 3 ganks in the game so you really need to take advantage of it. Make sure you don't get greedy too, losing your double buffs on Maokai will set you really far behind. Also keep in mind that your flash isn't as valuable as a laner's flash. Don't be shy to flash Twisted Advance someone early game, they'll have to blow their flash and when they do, they'll be extremely vulnerable to ganks later on.

Your goal for this part of the game should be to stay as close to your lanes as possible, preferably middle and top. Wraiths are a really good place to be because you can easily get to mid and countergank or just straight up gank. Something you also want to do in this part of the game is keep track of the wards that are being placed. Totems from levels 1-9 only last for 60 seconds so if you see a lane warding, time that and make sure you gank when those 60 seconds have passed, it's usually a free kill and that's really all you need to get snowballing!

You're extremely strong in the mid-game as well. You need to capitalize on this by getting some early boots, if you're snowballing get Mobility Boots, if you're doing good, get Mercury Treads. Once the mid-game has come, objectives become a factor, you can force ganks really easily and by doing so you should have some opportunities for dragons/towers.

You want to get as many dragons as possible as early as possible so you can grow your advantage as much as possible. You fall off late game so this is a crucial part of the game where you are tanky, you deal a lot of damage and you can easily dive. The more you play Maokai, the more familiar you'll get with his limits, but he's extremely strong at this part of the game so make sure you take advantage of people being low at their towers or not having any form of escapes (flash burnt, heal down, etc.) Also make sure you do a lot of invading around this time as you're one of the strongest champions in the mid-game. This is your time to shine and get full vision of the enemy jungle, you can even counterjungle them without a problem.

Late game come, you're going to be a lot more of a damage soaker than anything else. You want to sit in front of your teammates to make sure they don't get caught by skillshots or poked. You also want to drop as many saplings as possible so you can keep some good vision on the map, you wouldn't want your team to get caught or facecheck a bush with five people in it when you can simply toss a 35 second ward (your sapling toss if you didn't get it yet...) to scout.

At this point, you're pretty much going to be all utility, so peeling is probably the way you want to go, unless you have a team with assassins then you might want to dive and root a carry, I'll talk about this more in the teamfight section though.

One last thing to keep in mind is that you're going to want to be grouped at all times in the late game, and that being said your passive will be charged to 5 stacks VERY OFTEN. You NEED to keep auto-attacking things to regenerate your health, you should be unkillable.

Knowing how to teamfight is really important on Maokai, and it's different every game. There are a few factors you need to keep track of and be aware of in your games.

First off, you need to know what kind of a team composition you have, if you have a poke composition (this would have champions like Varus, Caitlyn, Corki, Jayce, Nidalee, Syndra, etc) then you want to wait for your team to deal some damage before engaging. At that point you'd probably want to dive the lower targets or the more vulnerable targets (those with no escapes) and make sure their deaths are prioritized.

If you're running with a dive composition (this will usually have assassins like Zed, Fizz, Talon) you want to catch a target and nuke them, so you wouldn't really be peeling for anyone, you'd be going for a dive on the enemy carry (person who's the strongest on their team), probably the ad carry or the mid laner.

If you just have a standard team composition then chances are you're going to want to peel for your carries, the best way of doing this is just rooting and slowing people who are trying to dive them, it's a really efficient way of playing and is generally the safest way to play as well.