Well if you think joining the Church of Satan is a good way to get back at God, think again. They're not even real devil worshippers, they're just a bunch of athiests who wear silly outfits. Even if they were, Satan is on God's payroll, anyhow.
If you really want get back at God, succeed in life. The evil bastard hates it when humans manage to lead productive, fullfilling lives. Every bit of happiness a person feels inflicts pain upon the evil deities who put us here. I cannot tell you how to win at life. Hell, I'm trying to figure out how to beat it myself.