I once read this Paul McCartney interview where he said that "God" is just "Good" minus a letter, and "Devil" is just "Evil" plus a letter. He also said he doesn't really believe in God or the Devil, just the basic principles of good and evil. Whether you believe in God or not (or a different God/Gods), I think you should just be a good person. Don't kill, don't rape. If it's something that harms another person, it's bad. Don't do it. If there is a heaven, chances are you'll make it in. If not, at least you were a good person. People will remember you for that.