Pros

good ganks
mana regen passive
stealth
auto win games
scouts for unwatched enemy buffs without much danger

Cons

Very squishy in jungle early
not a lot of damage until you get sheen or triforce
very vulnerable to early level counter jungle

Passive:
allows you to have successful ganks every time
use it to stand behind enemies and wait till your lanes to engage first to proc the enemy cc or escape skills
use the stealth advantage to ward the enemy jungle, or stalk the enemy jungler when they are going for a gank

Q:
spam it, spam it, oh and SPAM IT!!!

W:
use it when you laners start engaging in fights
*be sure to stand close to the enemy in a range that you won't be noticed*
also a good skill for escape or catching up to an enemy.

E:
with triforce this skill will deal 'tons of damage'
and give you a decent amount of attack speed buff for 3 seconds
however it does not work on tower.

R:
slows enemy and gives you a decent shield
use it when are trying to run away or catching up

try to counter jungle as much as you can
very helpful in reducing early enemy ganks and allow you to have more xp