It won't work for everyone, especially if you don't have the patience or skill to hit at least every other spear. This build is very effective for jungle spearing (throwing spears in the jungle for max range/damage and getting away)

The sixth item tends to change whether or not you want armor (zhonya's hourglass), magic resist and lower their's (abyssal scepter), or you want to go for a possible one shot spear (rabadon's death cap) recently been suggested death fire grasp's active as a tool against tanks or for an easy kill + the ap. The reason I go with all the mana (and clarity) is that you can throw a spear every five seconds, so even if you can't hit every Javelin you throw, you deny them gold from minion kills just from fear and can keep them at bay until cougar form (Without having to go back for mana). Archangel's staff's passive can be fulfilled by Nidalee with almost no attempt in cougar form, since you'll pounce every two seconds to get places faster.

Doesn't really matter if you lane or mid, the only difference will be how you position yourself and keeping enough mana to heal yourself and ally. One problem I find is that even doing half of an AD carries or mages health with one spear, it is very hard to carry your team. Another problem is that if your kind hearted, you might get stuck in a support role when team fighting or team laning starts, as your heal will end up healing at least a fourth of your teammates health. Warning: you will be rather squishy, use your heal and range to compensate.

Nidalee's passive prowl(15% more movement speed in bushes and 2 seconds after you exit a bush) is the best escape tool she has, use it well and dominate the jungle with traps and speed. Her pounce(cougar form) can be used to hop over walls, but it is risky as she tends to turn when someone is attacking you (baron and dragon are very nice walls to hop over, especially against skill shot and aoe users) just keep in mind this should be a last ditch effort as you will have to wait two seconds to try again. If your damaged you may want to turn human and heal, try to avoid this unless absolutely necessary, stuns and other disables will probably end up getting you more damaged wait until your at a turret or teamates (or have successfully juked) to heal.

A. aim for where they are more likely to be, not where they are at.
B. if someone has been dodging your spears most of the time and they randomly decide to stand still, they are trying to make you waste mana and will likely dodge the spear
C. try to strike at random and from different angles (and try not to be to obvious)
D. Minions will block your spears, so turn a disadvantage to your advantage, get a minion in front of you and attack it they will likely go to get some gold from minions and as your final shot hits the minion, throw a spear, they likely won't be ready for it thinking the minion would block it.
E. Use your traps for more damage and keep them at a range.
F. This should be a no brainer, but the spear does more damage as it flies, try to hit maximum range.
G. Don't be afraid to guess and throw blind, it can get you kills or at least gold.
H. USE the Javelin's and traps to probe, it'll be near impossible to gank your lane if you use the bushwhack consistently

A:keep in mind that with this build you are squishy
B. if they get on half health, try pouncing clawing and then popping the takedown for a possible kill.
C. if you want to kill minions fast, cougar's the way to go.
D. keep in mind the slight cooldown between going cougar and going back, be prepared for no heal and no spear for 3 seconds.
E. Use pounce to dodge skill shots
F.They will treat you like a mage, use cougar form to surprise them when they're on half or less.

Ezreal- his flash ability will close the distance on you to well and can be used to both dodge spears and damage you.
Leblanc- cause she's just op
Brand- any decent brand can stun and slaughter you.
Akali- her dashes will slaughter you and she can go invisible making you blind. She is this builds kryptonite, HOPE THERE is not an akali.
Sivir- (hardly pops up but...) her spell shield will be easy to pop, she can chase you even in cougar, and her attacks can hit you through minions.
Teemo- any good teemo that is, he will beat you at the trap warfare and you'll never have a chance in cougar form unless you get him to a third and he doesn't blind you first.
There may be others, but I can't remember or i haven't fought them yet.
And Tanks in general will stop you from getting kills.

AD carries- they often do a lot of damage right? well with this build if you keep your distance and hit them with the max range spears, they will find a third or more of their health gone per spear. One that you do not want to mess with is Yi, as he has the ability to hunt you down with highlander.
Mages- if your midding, you'll likely go up against a mage, if you switch to cougar and rush them, they will not be able to take you, beware of disable, and try using your spear to finish instead of chasing.

I use those runes so that I won't run out of mana and because I buy Archangel's staff.

Clarity for sure
Ignite- if you can hit spears, you won't need it.
Flash- convenient, but long cooldown
Clairvoyence- not as nice as it seems like it'd be.
Heal- yours will do more and has less cooldown.