If you find a tactic that really gives your opponent trouble, do some serious thinking about how often to use it. You may have two options: 1) use the tactic to win one game; or 2) use the tactic to win the match. If you want to squeeze an entire match out of the winning tactic, then you don't want to overuse it and allow the opponent to get used to it.
For example, suppose you have a serve your opponent misses over and over. Unless the opponent is brain dead, if you overuse this serve, he'll get used to it. He'll also expect the serve at key moments - so you have to decide whether it will still be effective at that time. If he hasn't made many good returns of it in the past, then he'll probably have trouble with it under pressure as well, so most often use it at these key, pressure-packed points. When he does make a good return of this serve, hold back on it for a while, and then surprise him with it again.
If you only have one serve that gives the opponent trouble, perhaps you can turn this into two by doing some variation of the serve? A different spin, speed, or depth, or even serving from a different part of the table might be enough variation to allow you to use it more often.
Suppose an opponent with a big loop keeps missing when you push heavy to his backhand. Do you really want to warm up his attack against this by giving it to him over and over? I've had many coaching experiences where a player went to the well too often, and tactically had nothing left in the last game. I once coached a match where the opponent had a huge backhand loop off a deep push to his backhand to follow up his short backspin serves. In the first game, the opponent missed over and over. Between games I suggested using the tactic at the start of game two, then holding back on it a bit, perhaps pushing more to the forehand, pushing short, or flipping. Instead, the player I was coaching pushed long to the backhand over and over, took an early lead - and then suddenly the opponent's big backhand loop started hitting. Afraid to push deep to the backhand, my player started pushing to the forehand, where the opponent was even stronger. Afraid this late in the match to start flipping or pushing short, my player fell apart, and the rest of the match was a rout.
It's important to come up with several winning tactics, and vary them. Experiment early in the match, and find what works. If you have one serve that works, find a variation of it so you have two. If you have two serves that give an opponent trouble, go back and forth between them somewhat randomly, mixing in other serves as well, perhaps looking for a third effective variation. If you build up a lead, perhaps temporarily retire one of these serves for later. But be careful - don't blow a lead by failing to use what was a winning tactic. It's all about judgment.