Unless you have a lot of experience in meditation, jumping straight to the 'clear my mind' thing is tough.
I have found that having a focus works best for me. It can be a mantra, or for me, counting breaths. There are couple variations on that:
Count on inhale (1) and exhale (2) or count the inhalation and exhalation as one. Either way, don't attemtpt to control your breath, just be aware of it and count. Count to ten and then start at one again. When your mind wanders off, note that it wandered and begin counting at one again.
This has proven to be the simplest and best meditation technique for me.