Mark Of The Assassin (Q)
Shadow Dance (R)
Twilight Shroud (W)
Crescent Slash (E)

After this, if the enemy decides to fight back, spam your Q and E while making sure you use W as much as you can. If the enemy decides to run, make sure you mark him/her with your Q then R to them as fast as possible.

The tenacity buff, even though it's not much, it still helps if you run out of heath potions or just need a bit more health to harass your enemy(s). Now in the new patch, it helps because it is the path to Vampiric Scepter which is used for the gunblade.