If you're giving homework like a written essay for example, let them choose from a list of topics. Or, if they're doing a speech, allow them to choose just about anything as long as they check with you first before starting. For a group project, give them guidelines and recommendations but don't micromanage how they get it done. As long as the final result is what you're looking for, it doesn't matter how your students get there. Their process may be different from yours, but that's okay.