Sam Harris has posted an excellent lesson on mediation:
I thought it might be interesting to show how I meditate, as my method is, I believe, much easier. A couple of years ago I was taught how to get into a state of mindfulness by therapists, and it's something I do these days to calm my mind. I find it very relaxing and peaceful. This isn't like other approaches to mindfulness I have come across, as I don't focus on the body.
First, get into a situation where you can relax. This can be sitting, lying down or even standing. What matters is that you can comfortably remain in that situation. Now find something visual to focus on. It should be something simple and calming, such as a tree out of the window. It doesn't really matter as long as it's simple. Now while staying as relaxes as possible focus your attention on the object, while working to keep your mind clear. As soon as any thoughts come to mind (and they will), dismiss them. If your attention wavers from the object, draw it back gently. The aim is to be focussed on the object while thinking of as little as possible.
What can happen after a while is you start to lose a sense of time and self. You may find new perspectives of the object appearing - you may, for example, have a sense that a tree is filling your field of view even though it's far away. Most importantly you should be in a state of calmness and peace, and there will be a wonderful feeling of mental relaxation.
Don't worry if this doesn't happen. It will take practice and it may take many minutes even when it does. What is beneficial is the act of working to clear your mind, learning to control your thinking.