Well, the first insight about meditation is that you can't just think of nothing and let your mind go blank. Thoughts arise spontaneously; you can't suppress them. Instead, observe your thoughts but don't become attached to them. Recognize them for what they really are: just sounds and images that arise on their own and will drift away on their own if you let them.

My favorite metaphor is to imagine that thoughts are bubbles and your awareness is a feather. As the bubbles arise and float toward you, you very gently deflect them with the feather, without popping them, and let them float away.