Write. Disclose memories. Share the fiction of your past. Invent memories. Pretend to be the friend sitting opposite of you. Hide yourself. Deconstruct yourself. See how your friends imitate you. Appear as someone else. Fail to be recognized. Hear your friends discuss patterns in your behavior. Be nondescript. Listen. Think about your friends. Identify your friends. Notice your friend trying not to be identified. Catch your friend pretending to be someone else. Catch your friend trying to be you. Estimate the extent of your knowledge. Predict how well your friends know each other. Speculate. Be wrong. Be discovered. Read. Acquire information. Win.
If this sounds fun, perhaps you would like to give Memory Match a try. The game is still in development, but if you and your friends would like to be guinea pigs, it can be arranged.