Doing regular exercise is something that every person should do. I found out the hard way as I packed on pounds of fat and slowly buts surely became more and more unhealthy. If you can help it, do not let this happen to you. It's far better (and easier) to maintain a good fitness level, then to work your way up from the bottom. And with the right goals and work ethic, you can reach almost any fitness goal you may choose to set.
When your just starting out, you should make sure you know what you are aiming for. Because of course you cannot hit a target if you don't know what or where it is. Now you may not know 100% what you want to get out of your time spent at the gym. But for the time being, you need to put something down on paper as a way to wake up some motivation in you.
The goals that you set when your just starting out don't need to be long term or anything. In fact, they're just there to make sure you get your butt of the couch and actually start! So something like - start going to the gym 2 a week for at least 30 minutes within two weeks time. That goal will start you off and help you get past the hardest part of it all. Later on you can write up some long term fitness goals, but for the time being that is more than enough.
Your diet is critically important. The difference between a person with a healthy diet and one with an unhealthy one is huge (when all other things are equal). So you should aim to be eating a 100% healthy diet (or at least 95%) as soon as possible. The best way of doing this is by researching into all the difference foods that you eat and then cutting out the foods that are not good for you.
Okay, so at this point you are all set to start doing some exercise. Of course you'll need to take it slow when you first begin. It's smart to learn about each machine and how it works your body. You will then find it easier to plan out a workout routine which is the next step.
After you've been going to the gym for a little whole, you'll find that your ready to move onto the next step. So this is when you can begin thinking about combining certain exercises and creating your own workout routine.