My personal favorite way to play Venomancer: Transitioning from a pushing-oriented support hero to a surprisingly fast and unpredictable semi-carry capable of killing an entire team's worth of heroes.

In the early game, be judicious with your ward usage; your mana is limited, and savvy enemy players can easily kill level 1 wards for a pinch of gold. Later, when you have greater mana regeneration and higher ward health, spam them literally everywhere. Poison Sting can net easy kills from weakened heroes.