This is my first guide so go just a little easy on me. People say to me that Garen is no longer a tank, which in my opinion, is very wrong. His abilities/passive keep alive throughout most of the game, if not, the whole game. This is my take on how to tank as Garen. I get a lot more victories than defeats with this build. Even if it's a defeat, I have a very low death count.
(assists and kills usually balance out)

Pros+
-Early game domination with Q and E
-Looooong silence with Q
-Passive keeps you in lane a lot longer
-Can escape ganks before they happpen
-Catching enemy champs is easy as pressing Q
-Courage passive provides extra armor and MR
-Ult is a tank destroyer and stops escaping enemies
-Overall great tank
-Spin to Win!

Cons-
-Can be taken down during cooldowns
-Only CC is silence
-Can be dependent on laning partner to initiate
-Easily harassed by ranged DPS and casters
-Have to be careful with cooldowns
-Abilities are short range

Marks
Health: The main marks I use for that extra health neeeded early game. A little extra health early game can make a BIG difference on getting FB or just surviving a fight.

Armor: A 2nd option for your marks can be these if you'd prefer the extra armor over health. I'd use these if taking dodge seals instead of armor. Although the seals provide a way larger armor bonus than marks.

MagicResist: Another option, but I don't recommend it since, our glyphs are strictly MR. But as always, some people do prefer that extra MR or Armor over health.


Seals
Armor: My main choice of seal is armor. each seal gives about 1.5 armor to your already tanky self, making you harder to kill early, mid, and late game. Its kept me alive against those early dps carries like Master Yi, Xin Zhao, Jax, etc.

Dodge: A 2nd choice for players who like being able to dodge and possibly survive. I don't normally use these, for the armor is greatly needed to keep alive and dodge has only a small chance of occurring.


Glyphs
MagicResist: Having all 9 of these equipped makes laning against early game AP killers a whole lot more painless. Ex: LeBlanc, Swain, Brand, etc.


Quintessences
Quints: These can be done either way of 2 resilience and 1 warding, or 1 resilience and 2 warding. Or... 3 of either one. Your choice! ^_^

Not too much to explain here. I take a pretty standard tank 0/21/9. Obviously for Garen do NOT grab Ardor. He has no need for AP and attack speed isn't needed as much as extra dodge and Nimbleness. There isn't much point using the last 9 mastery points pushing down the Offense tree, since the most you would get there is attack speed, crit chance, or cd. Garen's cd's are already pretty low for a cd based champion.

Note:A friend stated to me that I should use the last 9 points in offense for the extra damage on Judgment and Magic Pen on Demacian Justice, also the cdr by 3%. I personally like the support tree better since, it gives me more hp5 to help in early game and a boost to Ghost. You can go either way.

Which summoner spells you choose can affect the outcome of any fight greatly.

Main Spells

Even though Garen already has a speed boost from Q, Ghost can make it extremely easy to catch up to someone (with Q too), escape, run over to help in a fight, chase down and ult an escaping enemy, and other things too.


Exhaust makes it even EASIER to catch someone, escape, and even setting up kills for teammates. (makes FB easy to get too)

Other options
Note:All spells listed in this category can replace either spell mentioned above or both.

I normally don't use it for all the speed Garen gets, but it can be used to teleport back to lane, towers under fire, ganking, etc.

If you still can't escape a gank or team fight and being hit with a bunch of CC, this is your ticket out. Prioritize stuns, snares, and slows first.

A substitute mainly for Ghost if you prefer Flash. Don't care to use it over the huge speed boosts you can achieve from Ghost. Can be used to escape, chase, gank, get in range for ult, etc.

For people who make mistakes, and can't keep the passive active while staying back.

Amazing if used at the right moment. Can save towers, and sometimes, even you.

Avoid

No, just no.

Best left for support champions.

Once again, just no.

Not needed as much as other spells really, at all.

Not worth it, save for a support.

Why?

One lovely thing about Garen is you don't have to worry about any AP, for, his skills do not scale at all with AP.

Skill Sequence:
E>Q>W>E>E>R>Q>E>E>Q>R>Q>Q>W>W>R>W

Skills:

Garen's passive is similar to Dr. Mundo's Goes Where He Pleases. Garen's passive gives him a crazy health regen after 7 seconds of not being hit.

This is where your escaping, chasing, etc. is from. This skill has so many uses. The long silence can keep champions like Vladimir Sanguine Pool, LeBlanc Distortion, Kassadin Riftwalk, etc. from escaping using their skills.

Here we have your tower diving skill. Your survival of that last hit. This is why Noxus could never kill Garen. This skill gives you a huge defense boost starting at 10% at level 1. This skill rises 5% every skill level till a whopping 30%! Also its passive gives you 0.5 MR and armor after every minion kill up to 25 at level 5 (+5 max per skill level).
That's about half the strength of an Aegis of the Legion but without the damage and health.

Here is where the phrase for Garen "Spin to Win" came from. Early game it destroys anyone and everyone. Mid and Late game it takes squishy champions down pretty fast for being a tank. Problem:Enemy champion walks into brush where Garen in waiting. Solution:Press E. End of story.

Garen's Ultimate skill is got to be one of the best killers in League of Legends. It already packs a punch each level, but the more health an enemy is missing, the more damage it will do. Any tanks who depend on health items like Dr. Mundo have to be wary when having low health.

Core Item Build


Buying this first at the start gives Garen everything he needs to succeed early game. It gives a small amount of armor and health. Also a little hp5 to help Garen regen faster with his passive after taking some blows.

Even more speed for Garen! Hazzah! These boots are just what Garen needs to make his Q and Ghost catch anyone, anytime, anywhere. Or even escape. But these boots can be replaced by Boots of Ludicity as a 2nd option. I go with Boots of Swiftness, for it you don't need the cdr to escape or chase. The extra speed gets you to them.

This item is amazing on Garen. It gives you the perfect balance of MR, armor, and health early to mid game since it takes small items of all 3 to make it. Plus! you get a little extra damage boost from the aura it gives. Your team will thank you in the end for the damage, MR, and armor boost you're giving them.

Not too much to say here how useful this is for Garen. More health. More armor. And the passive makes Judgment twice as deadly.

To balance out all that armor, why not a banshee's veil? It gives you extra health (don't worry about the mana), a nice MR boost, and will help against pesky casters with the skill shield.

Another large helping of armor and MR from this item. The passive is to "die" for. Literally.


Options for Last Item slot

Great item for any DPS champions still bringing hurt on you and your teammates.

Huge MR bonus, hp5, and a passive that compliments Garen's Perseverance. Great against casteres.

I wouldn't really recommend this as much as other items, for you already have a large health pool. Still an option though.

More health, more armor, more mp5. Plus some cdr that can come in handy. The passive will make getting away easier. The active will make it easier to do the chasing!

Although it gives mana, it gives a huge 99 armor bonus and 20% cdr. Makes DPS champions slower at attacking you when they are nearby.

Early Game

Garen dominates early game by far, more than most champs. Judgment can knock down anyone right as it activates. Surprisingly Garen CAN harass. Using the brush, you can wait until someone is close enough, Q your Decisive Strike and go take a whack at them. This does a fair amount of damage AND hands them a long silence, possibly stopping them from using one of their skills on you. Only try harassing if you know you can get close without taking too much damage or possibly none at all. After the hit you should be able to escape fairly easy by just running back into the brush. The speed boost should still be active from Q. If they decide to chase, start spinning with E and activate W for your shield and just spin away to the brush or to safety!
You will possibly be dependent on your laning partner to initiate the enemy or CC them. Which will enable you to Q to get in there, hit, spin with E and get out using W if needed. Champions with stuns like Evelynn, Sion, Annie, or Pantheon are great laning partners. They allow you to get in there without taking damage from the stunned champion. That does NOT mean you won't be hurt by the other champion laning with him (unless he runs, hehe). Other great champions are Shen, and Rammus for their taunts (probably won't happen since you are already a tank), Nocturne and Fiddlesticks for their fearing, or even champions with slow CC, will make laning a whole lot easier. They will also thank you for the Aegis of the Legion aura you'll have later in lane. (if your still in laning phase)

Mid to Late Game
The strategy for Mid and Late game is about the same. Team fights obviously start about this point, if not, later. You want to position yourself in front of your team so you can tank any skill shots they might have or other little things they might use to harass before the team fight initiates. Just be wary of any skill shot CC (ex. Morgana's Dark Binding) that will cause them to initiate. Champions with "mini-flashes" (ex. Ezreal's Arcane Shift, LeBlanc's Distort) or even Flash off cd might try to CC you also.
If a team fight ISN'T happening. It would be a good idea to push side lanes with at least 3 of the enemy chapions busy trying to initiate a team fight. Don't be too scared to push, just keep an eye on the mini-map to make sure no one ganks you. If you see someone move towards you on the mini-map or you think you've pushed far enough to where they've noticed, just run back to somewhere safe or hide and recall.

When to use Garen's Ult
The thing I hate most about people who play Garen is, they wait for you to severely hurt an enemy champion, then they come in and ult for a killsteal. That's not the point of his ultimate. It's used to stop other from kill stealing you, stop enemy champions from escaping that your allies can't get near anymore, or he's getting away while your allies are on cd with their skills. Here's an example of a good time to use it. Katarina uses her Death Lotus in the middle of your team, a few of you are about to die and she has about 1/5 health left or maybe more. Use it. Your teammates might call it a killsteal or complain, but you just saved their lives from giving her a triplekill! :P It's moments like these that make Garen's Ult such a viable asset to any team.

Thanks very much for taking the time out of your busy (I think) lives to read this build. If there is anything I could change, please post in the comments.