Discipline is a good starter for fitness. I think doing workouts as a routine helps a lot but you can't just jump in on day one and do a 2 hour workout and then expect to keep that level up all week. Start off in moderation with whatever you do then make sure you do different types of routines so that you can work on different muscle groups on different days. Your body easily becomes accustomed to your workouts so you need to confuse your body and change it up.
This is not to brag but I consider myself trim and fit. That's the result of 40 pushups in the morning coupled with the use of the hand grip exerciser. Not to forget that I do the normal warm up of bending and stretching. With the diet, I don't eat a lot and moderation is my rule when it comes to dining. I eat almost anything and I really don't go for healthy foods with no taste.