Start by gazing at a blank wall for 30 minutes. No, seriously, it's a skill. You'll be amazed at the things you can see. Or not see. Either way, it's a great way to spend your afternoon.
Now that you've mastered the art of staring, try it with a friend. See who can spot the most interesting things in a picture. Loser buys coffee.
For a real challenge, try using a Ouija Board. It's like a combination of staring and... well, staring some more. But with a spiritual twist.