1. Diet: just try to cut out processed foods. If you've managed to get through your 20s without turning into a lardball you're probably not eating that much more than you need anyway. 2. I assume you have some kind of smartphone. Download a few apps like 100 push ups, 20 pull ups, 100 squats, 100 sit ups. They will give you a program to follow for 6-8 weeks and will automatically generate logs and charts and things that appeal to the OCD. 3. For motivation, place a bet with someone obnoxious at work that you will not be able to complete the above programs, someone who will mock you without mercy if you fail. Your average law firm is full of highly competitive people with personality disorders so you should be able to find one. You should be able to notice the results after a couple of months, then you can try a few sports and see if you find anything you enjoy doing.