Three rules
Quick rules that I wanted myself and my boys to adopt. Tennis Make your serves count . Serve1 should be solid, serve2 should never fault. Focus on your strengths . If forehand is great and backhand is so so, then exploit forehand. Make opponent inconvenient . Make opponent run, place your replies such a way that opponent is always on the run. Make sure to shuffle back to baseline so that you do not do the running. You can run for some time, but get tired after that, but by running and playing , you mess focus and stability and you do mistakes before you get tired. Chess Analyze opponent step. Talk to your pieces and pawns if everyone is safe. Think about your moves. Check what you can move (options) and make best move.