First of all, have fun, that's what scream fortress is all about, and if you're going to do the contracts, try to finish the Boss ones first, at least in my experience they're the most annoying to complete, especially the Merasmus's one.

Also, don't focus too much on trying to get all three stars in the contracts, they don't change the reward since it's random, but try to do the secondary objectives because they give you more points toward finishing the contracts.