In addition to what Axeman said, your lighting should be as soft as you can make it. Harsh lights make it harder to key, in my experience. Two ways you can soften your light is either making a makeshift soft box (my preference, PM me if you want details) or moving you light farther from the object your trying to light. Also, when lighting greenscreen, I have found it most useful to use the normal three point lighting (key, back light, fill) along with a background
light, which is used to light the green screen itself, and brings depth to your key. So, you can achieve a great key with work lights, as long as you place them in the correct positions.
EDIT: I found an article that had illistrations of what I'm trying to explain.
Three point lighting plus background light (four point lighting)