Of course, whatever happens, you can't copyright an idea so the best thing you can do is get distinct branding and characters which can be trademarked. The game mechanic as well is something you won't be able to stop people copying. Probably the best thing to do is not even try.
Yes, by all means trademark that which makes your game unique, design wise, but you won't get anything popular if no one ever sees it because you're worried about someone copying you.