At the beginning of the game use Decay on the two ennemi heroes on your lane and take the Last Hits on creeps.
Use Decay to start teamfights on your lane with your teammate. It will be easy kills.
Your abilities needs much mana so buy first Arcane Boots so you can keep spamming Decay.
Because you fight in melee Blade Mail will help you to make some easy kills.
For the Late Game you'll need to get Shiva's Guard to slow your ennemies down and get some armor.
If you know how to use your abilities and stuff it will be easy for you to be Dominating.