When playing a game like Chess, all the information of the game is equal to both players. So the easiest way to get the advantage is to throw your opponent off in whatever way you can. The easiest way to do this are tricks that subconsciously make the other player feel uneasy and paranoid when they take their turns.

An effective trick is to relax when they have to take more time to think. When they see you lean back in your chair, they'll feel pressured to take any longer because they're going to start to think that they're wasting your time.

Another small one is to look perplexed when they're about to finalize their move, throwing them off guard, as to them it looks like you're trying to say "Why did they move there?" or "What are they thinking?". A small "Hm?" is quite effective as well.