There's a myth that top players use complicated tactics to defeat opponents. Perhaps as they are about to serve they are planning out their first three or four shots? After all, chess players plan things out many moves ahead, and table tennis has been called chess at light speed.
That's not what happens in table tennis. Top tactical players don't work out complicated tactical schemes; they look at all the complexities and find simple patterns to disarm an opponent. There are just too many variables to plan too much. It's better to focus on a few simple tactics that will tend to favor what you want to do. The key is choosing those few simple tactics. That's your primary goal in the first game of a match, equal in importance to actually winning that game. Some tactics are for setting up your own strengths. For example, if you have a powerful loop against backspin, you might serve backspin so you get a lot of push returns. If the receiver pushes at wide angles, you might serve backspin low to the middle, thereby taking away some of the angle. If you have trouble with heavy backspin, you might serve no-spin, which is more difficult to push heavy. (If you fake backspin and serve it low, it'll usually get pushed.) If you have a good smash, you might serve varying sidespin and topspin serves, with varying speeds and depths. If you are quicker than an opponent, you might serve topspin so you can get right into a topspin rally.
Other tactics are to take away an opponent's strength. For example, if an opponent has a powerful forehand, a simple remedy would be to serve short to the forehand, and then attack out to the backhand, thereby taking the forehand out of the equation. If an opponent has a strong push that is difficult to attack, then serve topspin. If an opponent has strong side-top serves and a good follow-up, then focus on returning the ball deep. If an opponent has a strong forehand and backhand, perhaps go after his middle, the changeover spot between forehand and backhand. And so on.
Similarly, you can use tactics to play into an opponent's weakness or to avoid exposing your own weaknesses. See if you can come up with your own list of tactics of this type. Ideally you'll learn to play your strengths against an opponent's weaknesses. But sometimes you'll play your medium shots to the opponent's weaknesses, or your strengths to the opponent's medium shots.
Most top players focus on just a few tactics - perhaps two or three serve tactics, one or two receive tactics, and one or two rally tactics. This doesn't mean they don't use other tactics as the situation comes up, but they are standard tactics that are ingrained from years of playing and thinking about the sport. The specific tactics against a specific player are far more limited, and yet, if chosen properly, will pay off dividends.