Edit:getting 2 ranks of heal first makes you UNKILLABLE in a lane unless you make a mistake or they hardcore gank you.
Items: Doran's ring, glacial shroud, boots of mob, glacial>frozen(for hardcore tower dives and tanking towers during pushes), gaurdians/banshees, banshees/gaurdians, thornmail if phys team, if not start getting pots of fort.
Summoner Spells: Cleanse, exhaust.
Masteries: I like going down into utility just to get the mastery and the rest in defense to get vet scars and cleanse cd reduction.
Reasoning: Nidalee doesn't do a lot of damage from her auto-attack and her scaling with abilities is VERY poor. Her primary burst is in takedown and most people will assume you are squishy and focus you hard, if you are tanky it is quite surprising and you can still dish out a ton of damage from your naturally high takedown skill. Just be sure to switch out of forms to heal/buff and keep traps EVERYWHAR for map awareness.
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Put a point in trap. Then go for Javelin/Heal depending on whether you are being successfully aggressive or having to play defensively. Upgrade Cougar as it becomes available, and leave levels 2-5 of trap until very last.
Items: There are some good guides in the Guides section for this. This one by flankd has an item build closely resembling what I like to go for (Attack Damage over AP).
Sheen early is nice, Mobility Boots are nice, BF sword is nice. Triforce is also useful, because Nidalee has no CC (Leave the Zeal component to last, phage is much more useful).
If you're getting lots of kills, throw in a Mejai's.
I've experimented with rageblade... Useful, but not a priority at all. Doubtful any game will last long enough for you to get this far though. Survivability is also a good option (Banshee's, etc.).