Well,in team fights you can't just use Cougar Form and attack or you're gonna die.You're main role wil be spam your Heal (Primal Surge) and your Spear.The key in team fights is to go as far as possible for the extra damage.

Well,since the new patch the offensive tree is so good for AP.When i tried this mastery tree my damage was really high combined with the runes I mentioned.Basically,what you can do is instead of putting 3 points in Meditation you can put them in Swiftness.In my opinion this regen is really important in early game because you're gonna heal more which means for farm plus more harass.In my opinion Nidalee can escape pretty easily and doesn't need Swiftness.

You can either max your Q first or your E.Like i mentioned I prefer to make my opponent play defensively with my spears.If you feel like you cant outdamage you and you have to recall really often then max Primal Surge.

Why so offensive runes?Well you're going mid you can get Magic Resist Glyphs too.Although,I prefer to to have these so with one spear I will force them to recall so they will lose CS and exp.

What's the plan?Get Rabadon as soon as possible.Now about the boots...you can get these boots or Mercury Thread's depends if the opponents have a lot of CC (stuns etc).Last item I would suggest you to get a defensive item.You can either get a item for more armor or magic resist based on the enemy team comp.

Flash
That's the summoner spell you will ALWAYS choose.

Teleport
If you go solo mid or top.Teleport is really important for many reasons like not losing exp and CS or going fast drake.

SITUATIONAL SUMMONER SPELL:
Clairvoyance
If your team doesn't have a CV then you must take it.Really important and map awareness is the key to victory.Also you cav use it offensively like scout if they recall and throw a spear at them.

What you're also try to do is get the blue buff.It's just so great at Nidalee.No mana problems means spamming spears and heals which will result in awesome harass and almost always full hp due to primal surge.Also,last hitting is really important.If you aren't last hitting you will get your Rabadon late and it won't end up so good.

How to use your cougar effectively in laning phase?Easy,while you're farming use your W to go closer to your enemy then Q and E after these you must go back and continue farming.This is a great combo that will do tons of damage.What you do in team fights?Stay back use your spears,try to keep your teamates alive with your heal and then use your Cougar Form to chase them down.