This question has been asked before :
There are many wonderful answers for the same question in this thread, all of them are great. Some present analogies about the human mind (brain) and the process of emptying it, and some of them offer and present several forms of meditation to overcome this problem ( do something with the problem of clearing the mind) by practicing. Listen very well to Webstar and Othala, their posts definitely give you a great explanation and solution for your little problem of meditation.
My addition to this is not to try too hard to do what you call "clearing you mind", just take it easy and relax as much as you can and it will most definitely come naturally. Meditation should be a very released and relaxed process, trying intensely to get to the state of a clear mind won't help it at all. As you relax yourself and take everything easily, you will get all you need from meditation including the state of a clear mind. That is the general idea of meditation.
Additionally, there are plenty of meditation techniques and if this specific method you're attempting to use doesn't work for you, the easiest thing you can do is to look for a technique which is best for you out of those myriads of methods.