Look at myself in the mirror and ask what can be improved. Despite the belief that people should be happy about their bodies, I'm doubtful that there are many who wouldn't change something about their own body if they could. This can be dangerous if there aren't checks put into place beforehand, but if you're seeking motivation that can't be quantified, this is something.
As for gaining muscle, you can definitely quantify your goals. Just see where you are now and make a goal on how much weight and reps you'd like to be able to do per each exercise.