All sports involve collaboration, and table tennis is no exception. In fact, due to its one-on-one nature, table tennis in particular fits into this mode. One obvious collaboration is between coach and student, but there's an equally important one - between playing partners.
If you want to improve, players need to work together, both at the table and off. At the table, players can both play matches to improve their games, as well as drilling together in ways that both improve, often with players taking turns doing drills that the other needs, though both should be improving from the drill. But often the key difference between those who improve some and those who improve greatly is how far that collaborative process goes - does it end at the table ("some") or does it continue away from the table ("greatly")?
Away from the table, successful playing partners discuss and critique their games. If you played a practice match and found that your partner's receive was somewhat predictable, or that he had trouble covering, say, the middle or wide forehand, or that his backhand attack was erratic, or anything else - tell him! If you think his opening loops were too soft or landed short, or that his serves too often went long (or too predictably short), or that he telegraphed certain shots - tell him! This is not criticism, it's critiquing: "to evaluate in a detailed and analytical way."
And since this works both ways, you will profit from your playing partner's critique of your game. If he points out a problem with your game, listen to him - as your playing partner, he gets to play you regularly, while you don't get to play yourself. He has a unique perspective.
Critiquing is not all negative. One of you might see in the other something that has great potential, and so suggest developing it. For example, your partner might say, "You have such a strong attack - you should play more aggressively when you are serving." Or you might tell your partner, "You have such a strong backhand, you shouldn't try to force the forehand so much." And so on.
Of course, you could take the short-term selfish route and not make such helpful suggestions to your playing partner, in the hopes that you can continue to beat him - which means you will have a weaker playing partner, as opposed to an improving one, where you can improve together. Plus, if you aren't helping him in this way, why should he help you?
Take the long-term route, and make a habit of discussing each other's games with your playing partners. Turn it into a long-term partnership where both benefit and both improve. The icing on the cake is that by regularly analyzing each other's games, you become better at doing that, which improves your tactical skills in other matches, thereby raising your level of play even more.