AP nid is kinda weak right now, especially this meta, so don't feel bad if you can't do well with her. I posted a description on what you can do with AD nid top though: http://boards.na.leagueoflegends.com/en/c/tips-tricks/45lnZn1N-double-standards-how-do-i-play-nidalee-and-how-lane-vs-a-tryndamere-help-a-silver-scrublord
However, if you're adamant on AP nid, just keep a note of her downfalls.
-Spears, her main harass skill, is hard to land and easy to avoid (hide behind minions)
-She has no human form waveclear, which makes the enemy push minions to your tower, thus making last hit harder and losing turret hp.
-If she goes cat form to waveclear, she is highly susceptible to enemy harass.
-She is squishy and blows up quickly, mid laners tends to be nukers/assassins
So in essence, you can't start anything until the enemy screws up, for instance, if an enemy misses their skills. Nidalee is good against champions like lux, brand, etc. Lets use a caster type as an example: Zed
-He misses a shadow>shuriken combo and wastes his spinning slash on minions
-You either (R>W) to dodge or he just misses
-If you used R>W then move towards him R>Q>R>W>E>Q (Hitting a spear refreshes cooldown on R)
-If he missed and you're in human form then E> AA(Auto attack)> AA> Q> R> W> E> Q
Always E first unless you're sure you can just kill with a takedown (cat form Q)
If you're certain he/she used their cooldowns; don't be afraid to jump in on them in couger form W> E> Q does alot of damage, it just leaves you very vulnerable to a counter attack.
In terms of build, go
if you're very confident in lane, if not go
against AP and
against Ad (like zed yasuo, etc). You will need either
or
but never both. Afterwards good items are
,
,
,
,
,
, 
If you're dominating early on but have concerns for the future going
isn't bad, but defensively going
,
,
,
is recommended. Should have atleast 1 defensive item, unless you're doing really good and
and or
is enough.