There's a pretty good book called The Power of Now, it's not really mediation related, but it involves learning to live in the moment and to remove the past and future from your mind allowing you to live in the now, which is essentially what you want to accomplish. Nothing else matters but what you are doing now. There's some spiritual mumbo jumbo in it, but there's also a lot of extremely good stuff to learn from it.
I basically taught myself to clear my mind from complete thought and to focus on the moment. There are many different methods of meditation and you can easily find some simple ones on the web, but the main thing to know is to focus your mind on a mundane task so that the rest of your body and being can be clear and focussed. Everyone always says the biggest hurdle in weight lifting is mental and this is a big part of it, clearing doubt and confusion and negativity from your mind so you can accomplish your goal at hand. This transfers over to every aspect of your life as well, once you do it for a while you'll start to notice you don't stress out as easily or worry about things as often, it's extremely beneficial and I highly recommend it.
