***Rend (E)***
-Auto attack a minion to stack spears and leave it dying then either:

a.)
Auto attack enemy champion few times and cast Rend(E)
[*] Note: Don't get too far from the dying minion when casting Rend, else, you won't get Rend cooldown reset. Do this more often than option b just in case enemy chases you, you can auto attack him again and slow him with Rend(E) then flee - or auto attack him(when he is low on health)with the recent Rend slow and get chance to kill using again your Rend(if successful at killing minion with Rend).

b.)
Position Pierce(Q) properly to transfer stacked spears from minion to champion.

***Pierce (Q)***
-Use this ability to engage and disengage. Use this ability also during combat to maximize your overall damage.
-Never use this if you are only to kill a minion and not transferring stacked spears to enemy champion.