Pull Ups
This is a simple exercise that can give your upper body and arms a nice little workout. All you need is a bar suspended in the air. Most local parks have these on the playground. So there is no excuse not to workout. Just head down to the park and do a few. Below is an example of some more advanced techniques to motivate you a bit. You might want to start with the basics. Even if you can not do but one, practice is the only thing that will get you to doing more.