"Just do it" is probably the best advice I can give. You want those muscles or you want to get rid of that fat? Whatever the goal is, get up, find yourself where you need to be and do what you need to do. After a while it becomes habit and you don't even need motivation.
But sometimes we do need that initial push. You have to have clearly what you want in mind, know the steps necessary to achieve and tie it in with a sense of realistic expectation. Then just do it and what you want will come.