Shot selection can be the key determinant between winning and losing in most situation given players of equal ability. Sometimes it will superceed a higher quality shot maker who plays without a plan.
One of my cardinal rules for playing singles is using the 3 feet rule. If you are at the baseline, hit around 3 feet high crosscourt 75%-80% of the times for safety, margin and depth.
If you are inside the baseline moving forward 2-3 steps, hit down the line 75%-80% of the times no more than a foot over the net. Hitting the ball lower to the net will help you increase your effectiveness of your offensive shot by lowering the chances of the ball going out and your opponent having to rush to counter with a passing shot.
You may choose to follow it into the net or stay back. Having a disciplined model for shot selection will help you simplify the game, improve your execution and improve your results over time.
Feel free to reach out to me with any thoughts.