Heat, heat, and more heat.
It’s been my experience that gas burners are really the only way to get your pan/wok hot enough for a good stir fry. If you don’t have gas burners, work in smaller batches. We have a glass-topped stove, and it seems like no matter what type of pan I used, something was just missing from my stir-frys. Then my parents-in-law got me an individual propane burner for my back porch, and that became my go to stir-fry station.
I think a real wok isn’t exactly necessary for a stir-fry, but it sure seems to be easier cooking in one. The large size of the wok makes it easier to get the items in it moving around.
Don’t crowd the pan/wok. Over crowding means more heat being transfered to the food, and less heat in the pan/wok, and that leads to soggy over-cooked vegetables instead of the slightly charred, crisp, fresh tasting ones that a good stir-fry is known for.
Cook fast. Have everything prepped and ready to go into the pan before you actually start cooking. There isn’t a vegetable out there that when properly prepped, should take more than 3 minutes to cook in the wok. Better underdone vegetables than over done is my take on it.
I usually season very simply for our stir-fry. Nothing more than a dash of salt, or soy sauce. But if you’re going to use a teriyaki or some sauce, put it in about 30 seconds before the dish is done, toss the fry a couple of times, and remove. Many of the traditional off the shelf sauces (this includes meat marinades) contain a sugar, and can burn quickly at high heats.
Our favorite stir-fry that I make pretty often includes button mushrooms, zucchini, yellow squash, onions, and bean sprouts. Another we like is julienned carrots, sliced cabbage, and bean sprouts. Sprinkle with toasted sesame seeds and serve.