Smitty, there are two bedrock principles for getting in shape:

Do something (fast walking, running, bike riding) that gets your heart rate up and keeps it up for at least a half hour, and do it at least four times a week;

Keep at it religiously. Don't let anything get in the way of your daily (or four times weekly) routine. It's more important than having lunch with your friends, watching a movie, etc. Remember: you're doing it for you.

Most people agree that swimming is the best all-around exercise because it's cardio intensive, works all the large muscle groups, and isn't at all stressful on the frame or joints. Problem is: if you don't have your own pool, you'll have to swim at times and places not of your choosing. The most efficient and repeatable cardio exercise is indoor cycling: not expensive, under your own roof, you can do it day or night.