Another trick I’ve learned from my roommate: when stir-frying, don’t forget to add a little corn starch! Take a small amount of cornstarch (say a teaspoon) and mix vigorously with an ounce or two of water until it dissolves, forming a smooth paste. Add this mixture to your stir fry during the last couple minutes of cooking.
Here’s some “twice cooked pork” before and after pics to illustrate the difference:
This could be an “eye of the beholder” thing, but for me the second picture is quite a bit more appetizing. The corn starch not only adds an appealing gloss, it also acts as a thickener. All of the flavorsome liquids that you might add to a stir fry (oyster sauce, soy sauce, rice wine, etc.) bind into a delicious sauce coating the other ingredients. Bringing it all together so to speak. Beautiful!