You have to start small. The point of most meditation is to reach samahdi, which is basically where you think about nothing at all. Try to just focus on one spot on the floor or on the wall. Sometimes breathing out while making a sounds helps. Also if you want, try to close your eyes and picture the numbers one through ten. Count up by one for each inhale, and as you inhale try to picture the number coming toward you. Some styles differentiate between open and closed eyes, but I haven't really ever noticed much of an experiential difference.