I am no expert but I have done some reading, made many mistakes, and taken a month of Thai cooking classes with someone who is an expert. Below are a few things I've learned along the way.
1. Stir-frying is a very quick, high-heat cooking method so it's essential to slice and dice the veggies finely as they will only have minutes to cook, at most.
2. Peanut is the best oil to fry with because it has a relatively high flash point (the temperature at which it will begin to burn and smoke) compared with other oils. My brilliant Thai cooking teacher, Kasma, prefers lard over all else, but most people are sort of turned off by that so peanut oil is a good alternative.
3. You must have ALL your ingredients prepared and at the ready when you begin since things get pretty hot and heavy in the kitchen once you start stir-frying and there is no time to be cutting or mixing things.
4. Begin by frying your "aromatics" -- ginger, garlic, chili pepper, etc., in the oil you'll be using to stir-fry for about one minute. This will allow them to infuse the oil with their tastes. I owe this tip (which is probably completely obvious to anyone of Asian descent) to Deborah Madison's wonderful cookbook, Vegetarian Cooking for Everyone.
5. Remember the "order of operations" from math class way back when? In order to ensure that everything gets done at the same time, you have to start the things that will take longer to cook (like carrots) before things which will cook more quickly (like snowpeas).
6. Don't leave food sitting in the wok as it will probably get discolored by the metal fairly quickly.
7. Season your wok after each use.It's smoky and kind of a pain but absolutely essential.
N.B. Unless you are lucky enough to have a really good, high-powered stove (I'm lucky if mine even lights), you probably won't be getting the most out of your wok because they perform best over really high heat and your typical MagicChef burner simply cannot muster a super-hot flame. This does not mean you can't stir-fry with success but it does mean you may need to cook in smaller batches since your wok won't get as hot as it would over a really big flame.