Alright, you're going to need some things.
Go to Wal Mart, first.
You're going to buy two things:
1. A cheap pull up bar for your door frame.
2. Two sets of dumbells, one 'light' and one 'moderate' or 'heavy', or any combination of the three
Somewhere in your day, at the SAME time EVERY day, incorporate:
-Two sets of pushups
-Two sets of crunches or an abdominal exercise of your choice
-As many pullups as you can do
-Dumbell curls or hammer curls
-Shoulder flies
Start with this and go for a month to build a habit of exercise. DON'T YOU DARE DEVIATE FROM YOUR ROUTINE!
You will discover results, but you will also discover, if you are like me, that this is unbearably boring.
So I posit to you two things to continue your improvement, both of which are fun and effective. Do one, or do both.
1. Buy an actual mountain bike, go spend some real money on one made somewhere besides China, like Trek or Kona. Now talk to your local Forest Service office, or look online, and find the closest trails. Ride at least once or twice a week.
2. 'Acquire' Tony Horton's P90X workout program (not that I would suggest stealing it through, say, a bittorrent download as opposed to paying $200 for it, but that is always an option). You already have all the equipment you need to start doing it, since you bought some weights and a pullup bar. Just do as much of it as you can.
P90X has been criticized by weight lifting enthusiasts. But you know what? The facts stand on their own:
-The program has gotten countless people off their couch to SLIM DOWN and GET IN SHAPE.
-The program is FUN, it is ENTERTAINING, and there is a ton of variety in the program from classic lifting to
yoga. I LOVE the Yoga. And it DOES produce results. Just search 'P90X Results' on Youtube.
-It will absolutely challenge you. You won't get gigantic, but you will add bulk and you will look good.
I highly suggest doing both. You will love it. If you do start P90X or any other workout routine, I recommend a whey protein powder supplement to help with the muscles.
Whatever you do, dude, there are three things that are key to success no matter what anybody else tries to tell you:
1. You have to enjoy doing it and be doing something that is fun to keep your attention.
2. You have to be CONSISTENT. Working out every other week or skipping your pushups for three days won't do anything for you.
3. You HAVE to eat right. Good food does not cost more, because it's an investment. You might spend 30% more for real produce and fresh foods and take some time to cook them, but you are far less likely to incur cancer or heart disease in your life. And, it's a great life skill with benefits of its own to be able to cook (it's sexy

)
Good luck and let us know what you decide to do. But by all means, do
something. In a world full of diseased, unhealthy people, you really do have the chance here to become a beacon example of fitness and health.
Badjedidude said:
4. STRETCH! Always, always, always stretch before working out. A lot of people forget or neglect to do this, and they miss out of the benefits of it. Doing some simple stretches before an exercise or lift is SAFER, as it warms up your muscles and prepares them for action. It also helps to increase your flexibility, and acts as a cooldown AFTER exercises. Never hold a stretch for more than 10 seconds before exercising.
Oh ****, and THIS. So much emphasis on -this-.
Part of the nice thing about P90X actually is that it makes you stretch first. A buddy of mine neglected his stretching and actually hurt himself pretty good just doing pullups, knocked him out of his routine for about a month or so.
DON'T get hurt. ALWAYS stretch and take some good breaths, and NEVER overexert yourself whether in cardio or lifting. Regardless of age, you -can- damage muscles, joints, and other parts of the musculoskeletal system, and you can put your heart in to v-tach at any age (leading to a heart attack). Go for the gusto, but don't go past
(for a fella in his 20s, you dont want to exceed a heart rate of 160 really. Older you get, the lower that number goes.)