I don't main Nidalee, but I used to play her a lot in season one. Now that she can change into cat form at level one is awesome. I've played around 200 games with her and I can give you some basic advice that has worked for me.
My personal choice for summoner spells are 
unless you are support Nidalee then 
.
Barrier has saved me so many times and allowed me to change back into human form for the quick heal. (Get used to pressing ALT+E it's faster)
Practice your Q (Spears) as much as possible on moving targets. Just go into games and throw as many spears as you can. Take chances and learn the range and the hitbox. You will never be a great Nidalee player unless you are a master of the Q button. Once you have mastered the Q then learn how to master the Q with smartcast (or quickcast it's called now I believe).
Learn the best spots to put W (Traps). They will help your map awareness and can be used in conjunction with wards to make a very safe and secure lane. Always throw one near baron/dragon or even in bushes of the enemies jungle so you can see their jungler coming.
Get good reflexs and be fast with your E (Heal). Smartcast/Quickcast really helps with this. Heals can be the difference of you or your ally living and your enemies dying. With enough CDR and mana you can heal pretty damn well and deal lots of damage while doing it.
Now it's time for COMBO talk. Executing a full Nidalee combo can be devastating to opponents, but it takes a while to master and get used to the timing. Nidalee is a backline support/skirmisher who has mobility and can attack on the frontline, retreat and heal, throw a spear and jump right back into the battle.
Basically you want to throw a spear and hit a target (even better if they just walked over one of your traps) but the split second after your throw that spear you want to be in cat form, getting ready to close the gap with W (Pounce).
Your combo should look like this (starting in Human form). Q -> R -> W -> AA -> E -> AA -> Q -> AA -> R then quickly heal and throw another spear, get an auto-attack in if possible and then press R and back to cat form for a repeat. Very important to get the auto-attacks in. You want as much health gone for when your Q hits in cat form. Of course you must HIT your Q (Spear) in order to execute this combo, thus you must be a master of the Q button.
As for items usually play solid AP 
I absolutely love 
on her and sometimes I will play a hybrid AP/AD style.
Anyways I hope I gave you some useful tips. I am by no means a great Nidalee player, but I do enjoy playing her. Just keep practicing and develop your own style. Watch some streams of some pros and see what they do. Experiment with some builds and develop a solid combo that works for you. Good luck.
