Dark Matter:Use it withEvent Horizon, because then you can stun the enemy and this way it has more of a change doing damage to the enemy, if you do not stun the enemy before using this abilitie it has a small change of doing damage because it takes about 1,5 seconds before it is able to damage the enemy and its quite a lot of time, especially when you are facing an melee enemy, because they move around too much.Event Horizon:Use it then when the enemy is close to the beam surrounding the circle.Primordial Burst:Use it then when the enemy is running or has low health, try to use it more on AP champs.Baleful Strike:Try to last hit kill champions and minions with it, because for every minion you kill with this abilitie it gives you 1 abilitie power and then when you kill a champion with this then it give you 3 abilitie power.

PROS:
+Built-in hard CC
+A good nuker
+Easy last hitter
+Strong in 1vs1
+Good in mid and late game.

CONS:
+Bad in early game
+Long cooldowns
+Most of abilities focused on one opponent
+Only one defensive abilitie
+Not so good in 1vs1, unless he has ultimate ready.

Buy mana and AP, you do not need to buy hp, but when you are against Darius or someone who can pull you, and is melee it is recommended that you buy hp.