Common Fitness Goals
Repeatedly failing to stick to your goals means that either your goal is out of reach or that you haven't quite figured out what to do do to reach it. It helps to have a clear idea of what you want and the basics for what's involve in getting it.
Losing fat is probably the most common goal these days and, at it's simplest, involves burning more calories than you eat. If you burn an extra 500 calories per day, you would lose about a pound a week. You can't choose where you lose fat--Spot training doesn't work because your body draws energy from the entire body when you exercise, not just from the area you're exercising. That covers the basics and you'll find more detailed guidance in How to Lose Fat.
While weight loss is a common goal, there are plenty of people who have trouble keeping the weight on. In this case, your goal might be gaining muscle which, believe it or not, can be just as difficult as losing weight. Gaining muscle, like losing weight, requires careful attention to your workout and your diet with a focus on eating more calories than you're burning and lifting heavy weights. If you lift weights, you can build muscle but if you want to put on some serious size, that requires serious work, extra calories and commitment. Learn more about Gaining Muscle.
Training for a race or a sport often requires a different approach than if your goal were to lose weight or gain muscle. Your main focus should be on whatever you're training for. If you want to run a marathon, the bulk of your training will involve running. If you want to be better at basketball, your training will lean towards high intensity jumps, lateral movement and, of course, playing basketball. Whatever you're training for, you'll usually want to include cross-training. For example, you might lift weights to keep your body strong for running or cross-train with other activities to use your body in a different way and avoid injury. Learn more about Sports Conditioning.
Being healthy is probably the simplest goal to reach since there are tons of things you could do right this second to be healthy. Drink some water, eat fruit, take a walk, etc. Even a few minutes of exercise has a number of health benefits, some you experience instantly and some that may come over time. Learn more about getting healthy.