Nidalee has become one of my biggest main's and i love playing her mid. Now. Going mid as Nidalee is often disliked by team mates and enemies, but if you commit and play good, it will work damn well. What i also do, is play uber agressive and aim for that early game domination.
So if your more of a passive or defensive individual, i advice you to not use this build.

Now, the biggest reason Mid AP Carry Nidalee is often disliked is mainly because of her
passive: but as you read further into the guide, you'll see why i think Nidalee still has so much mid potential.

As i said, i go full out early AP agression, wich means that alot of people will probably not like these runes. Ofcourse you can always try new stuff, and adapt to what works for you and you're play style.

I go Greater Mark of Magic Penetration on red's.

I go Greater Seal of Ability Power on yellow's.

I go Greater Glyph of Ability Power on blue's.

And finally, i go Greater Quintessence of Ability Power on Quint's.

Now plz. before you straight up dislike the runes, plz consider that you can play any way you want here actually. You could go flat HP on Quint's for example.
Or maybe get some AP per level in there aswell. Its all up to you, and how you play.

This is the way i like it.

My Summoner Spells are pretty typical for a Mid AP Carry.
I go Flash and Ignite

Now, why do i go like this.
Its the same typical reason, you always wanna be able to Flash. Its a must.
And i take Ignite because i initiate at level 6, and at level 6 Ignite helps you alot at getting the kill on your enemy before he does the same to you.
(Even though most mid champions will have Ignite too)

What i see alot of Nidalee's use is Clarity
I dont like this one bit, even though i'm usually low on mana most of the game, but be sure to get every blue that is offered or available.
But i just think that Ignite is just that more important.

I go 9 0 21 on Masteries, wich is pretty typical and ofcourse taking Ignite and Flash in between there. And i take alot in mana, and mana regen cause as i said, i'm pretty low most of the game.

Not much more to say there, than that you choose what fits you'r play style the most.

On items i start with a Dorans Ring and then rush Sorcerer's Shoes
After that i go for a Rabadon's Deathcap
At this point, you should have quite alot of DMG overall, so now i build either a
Guardian Angel or a Banshee's Veil

And if the game is still going on, just build a Void Staff or a Lich Bane if you got enough gold that is.

All the core and main items are listed on top of the guide, keep in mind that those are only the core and main items, so ofcourse you will build in to them and not only buy those things, all depending on how well you're farming and such.

Farming on Nidalee is very important to be able to do, or on any champion for that matter
(exept for Support ofcourse)
But farming just gives you so much more. Back when i was kind of a noob i suppose, i used to think farming was just a little better, but not anything huge.
I was so so so so much wrong, just try getting almost every minion in a game, against a game where you have almost none, and you will feel so huge results.

So yeah, basically just try to farm every single minion you see.

Dont take any part of the jungle from you're team mates or jungler. Although be sure to always grab that blue when the jungler offers it to you. But always concider giving it to someone else if you have another AP carry on your team, that may need it.

Red buff is always good on Nidalee too, but i only take this in really rare cases, because you're most likely gonna have another AD carry on you're team, and you should rather let him have it.

Always buy 2-5 wards when you have the left over money. Always ward for yourself, dont expect the jungler or you're support to do it for you.

For example when you go back for you're Sorcerer's Shoes be sure to pick up atleast 2
Sight ward so you can push more safely.

In team fights there is actually a certain combo i use. Stay far behind while you're tank goes in, and the rest of you're team. Throw a Javelin Toss / Takedown or 2. Then, heal 1 or 2 people on you're team with Primal Surge / Swipe. Now you go all into the fight with
Aspect Of The Cougar.

This is the most efficient tactic i have found to use in team fights, but you'll adapt soon.

Nidalee will be changed in an upcoming patch. This will not have a huge effect on her, exept her Primal Surge / Swipe is getting weaker. But to make up for that, they are lowering the mana cost on Javelin Toss / Takedown and her Aspect Of The Cougar is getting more AP scaling, and more Armor and Magic Resist.

Overall i dont take this as a nerf. Im looking forward to try out the new Nidalee.
But i do believe that she will still be, and will probably always be a strong champion.

Overall. Play uber agressive.
If there is a squishy champion against you, take hits for hits. Its worth it, youll just heal it back.
At level 5, try to hit one or two Javelin
Then, after you hit level 6, you go all in with Aspect Of The Cougar and Ignite
and the kill should be your's.

Now in this guide i may have given the idea that i never back out from a fight or die first blood and such, but it happens. Sometimes you'll get outplayed. Its just the way it is.

Just dont give up, and keep playing Midalee and you got it :)