I've been playing Nidalee as my Main now for quite awhile and have had a lot of success with her using this build (about 150 wins and 20 losses.)

I feel like there aren't really that many good Nidalee builds at there and this guide will help you get not only good but if you stick with her, Great.

Pro's:
Great Harass
Amazing Sustainability
Unbelievable Mobility with Cat form
Once level 6 Almost NO mana problems
Incredible farmer once level 6

Cons:
Harass takes practice to land (spear)
If you spear too much Pre - Tear you will be mana hungry
Heal doesn't heal for much early on
Not much damage besides Spear Pre level 6

The reason I run 21/0/9 is Simple, it Gives you extra AP and some more Damage bonuses that you just wouldn't get if you used 9/0/21.

These runes ARE Important, with the Doran's Ring and masteries with these runes you will be starting with around 45+AP which works great with her spear early levels.

The Magic Pen Reds are good for the early levels and as well as when the enemy starts to get Magic Resist, just good all around runes to get.

The MP/5 per level Yellows are amazing on Nidalee, she is normally mana hungry and with these it lets you keep Tossing those spears and heals even before you get the Tear.

The Flat AP Blues and Quints are great all around runes for an extra AP boost early on and late game.

The reason I start out with a Doran's Ring is because it gives you an extra AP boost, health boost, and mana Regen boost.

As for the Fast tear, this is important because as Nidalee, if you play her right and aren't too aggressive, you will not need to go buy/heal unless you hit level 6 or you have around 3-4k Gold.

The Tear is AMAZING with Nidalee, when your in lane after level 6 (you should go buy the tear when you hit level 6) you can just go into Cat form and farm while ALSO getting the bonus from the tear, whenever you can use pounce to get you that 4 extra mana and usually you will never have any mana problems once you get this item.

The Boots, I get these because the CD Reduction is CRAZY on Nidalee, it helps spam her skills more without spending more money on other CD items.

By this point in the game it should be around 15-20 minutes depending on how fed you are and you should start working on the deathcap. Usually when I go back to get my boots I have around 3-4k gold and I get my boots along with a Needlessly Large Rod. Then once you have enough for your deathcap go back and get that. The extra AP bonus is a Necessity on any AP champion.

The archangel's staff gives you the extra AP from mana which by the time you get it should have the bonus maxed out and have around 2.5k Mana.

At this point the game should be rapping up or getting into a good late game, a Lichbane here is important because the Passive Bonus damage when your in Cat form does Intense amounts of damage.

After that just get a Armor/magic resist item, I prefer the GA for the passive revive, then another AP item if there's time left in the game, Usually the game will end before you get the Lichbane.

You should get your spear first for the early first blood attempt and just general harass. Honestly I laugh at the builds that say get your heal or trap first, the reason for this is because instead of having a 100-250 damage harass every 5 or so seconds, you could have a 80 Health heal every 8 or so seconds.

Most of the time to get first blood ( I play Nidalee bottom lane most of the time but she can be a great solo/mid) you want to sit in the bush closest to their turret, you can get there faster by hitting the little side bush for the passive bonus movespeed. Then your teammate and you should be waiting for them, when they are about to enter the brush throw a spear and toss on your ignite followed by some auto-attacks. If your teammate has Exhaust they should have used it, if they run they should be almost dead and by the time they are at the tower your spear will be up, usually if you hit this spear they will die if they haven't already.

As for the rest of the 1 - 6 Laning phase you want to be sitting in the bush most of the time throwing spears whenever you can at the enemy and trying to zone them out of XP while your lane partner gets CS.

Once you hit level 6 you want to Recall and buy a Tear.

At this point there will still be the laning phase and you will start to farm up with your Cat form. Just try and get as many kills on minions as you can while still keeping the enemies away.

You can gank from here but normally My teammate goes out while I hold down the lane and I keep farming.

By the time you hit level 11 you should have around 2k+ gold and you shouldn't have needed to recall because of your heal if you played it right.

You can recall if you want but there are usually teamfights that you want to be involved in.

By now you should have a good store of Gold saved up if you haven't died or needed to recall, you should go back and buy your boots/Deathcap if you haven't already.

Now its just mainly teamfights and pushing lanes.

When there's a teamfight close by try and throw some spears and heals out to help your team. I personally only go into Cat form to help when I know it's safe, if it's not it's better to just keep throwing spears and healing your team.

I'm not saying do this the whole game, yes go into Cat form and help but you need to know the situation and be able to read this. This will come by practice and you will know when to go into Cat form and when to stay in Regular.

I've gotten 1 Penta with Nidalee so far

Using this build you should have minimal deaths while also having Lots of kills/Assists.

Thanks for reading this guide, I will update it as Patches come Along etc.

Please post feedback on the guide with comments, Thanks!