Venomancer is generally played as a farming lane hero, but I felt like playing him as support this game! I find it more fun to max gale than to max wards, so I will do that while in pubs. If you do max gale, make sure that you max wards 2nd, after getting a few poison sting levels(max 2!). I went the wrong skill build this game.
In terms of items, a mix of mek, force staff, Urn, and Aghanihms Scepter are my favorites to get on Venomancer. Buy wards and things too!