Miyamoto Musashi was arguably one of the finest swordsmen to ever live. Born in 16th century Japan, he fought 60 duels (to the death) and won them all. He went on to write The Book of Five Rings, where he discussed philosophy, Buddhism, and combat strategy.
One of his core discussions in his writings is to never overuse one weapon – doing so is as bad as misusing the weapon since it becomes easier and easier for your enemy to find a weakness in your style. He was notable for using two swords simultaneously.
This lesson translates directly into tennis. I hear people saying “I need a weapon!” indicating that they want a powerful forehand crosscourt, or a powerful backhand down the line, or a powerful serve, etc. This is not the right way to develop. Obviously you want every element of your game, every shot, to be a weapon that your opponent is afraid of. You don’t want a weapon. You want about a dozen. If I only truly felt comfortable attacking with angled crosscourt forehands, soon enough my opponent would be able to anticipate that I would hit the ball there. They would begin moving before I strike the ball. It would begin to feel progressively harder to hit that shot and get them running, and I might have to try to hit it closer and closer to the line until I am hitting the ball out and making errors. Then my weapon is destroyed, and my confidence is low.
So stay unpredictable, have multiple methods for attack. Do not seek to simply have one effective weapon, but develop everything evenly. Naturally you will have some shots you favor over others, but do not over-use those shots or they lose their potency. If it seems that you are hitting good aggressively placed shots but your opponent is dealing with them just fine, try adding variety – instead of always hitting rolling topspin to their backhand, hit the ball to their forehand side as well. They may be moving before you hit the ball. It’s hard to identify when they have found one of your favorite patterns, and start to anticipate your shot selection.