As a coach and from my experience with over 10 years in the industry, I feel there are three main components in any exercise program to build lean muscle and lose unwanted body fat. These components are resistance training (lifting weights or using body weight), cardiovascular exercise and proper nutrition. All three are equally important in achieving your goals in fitness.
If one is not executed consistently, the other two will suffer and so will your progress. Don't get me wrong; to assume we can be perfect, 100% of the time will just be setting ourselves up for failure. It should be about progress, not perfection. Your goal should be to follow your programs the best you can most of the time. The longer the time you stick with something the better you will become at it. Here are a few ways we can remain more consistent with our exercise and nutrition programs.
Depending on your goals, you should perform some type of resistance training with weights anywhere from 3-6 times per week. The importance of resistance training is that it will help increase your lean, toned body mass, thus giving a better shape to the body and increasing your basal metabolic rate (look it up!). Muscle is like a 24-hour furnace, so we must be sure we maintain or even increase our lean muscle to keep the metabolism on the rise.
To help keep you more dedicated; I would find a workout partner or hire the help of a qualified personal trainer or coach. This way you are held accountable. I am more likely to workout if I know there is someone who keeps me accountable.
Cardiovascular activity is necessary to keep the metabolism roaring and help you burn some extra calories that will lead to fat loss. The main reason I choose to do a moderate amount of cardio is that it allows me to eat more food and still achieve the fat loss results I am looking for. Some people who rely on diet alone to lose fat usually find themselves losing weight but also a lot of muscle. They become a smaller version of their flabby self. Keeping a little bit more food in the diet, but using effective high intensity cardio sessions to burn more calories, will end up in retention of lean muscle while losing the fat.
If possible a few days per week, I recommend doing your cardio first thing in the morning, 20-30 minutes plus, before breakfast (fasted). This way it is out of the way, and it will really boost your energy for a good portion of the day to follow. It is a little tough in the beginning, but after a week, you will feel so good doing it, you will be locked in a routine.