Well, it sort of depends on WHAT you're stir-frying! But it's pretty straight-forward. Gather you ingredients and prepare them (chop, mince, etc). Heat a little oil in the wok. You can use sesame, peanut, olive, etc. Whatever will go with your ingredients. Add the ingredients that will take longest to cook (peppers, tofu, etc). If you are using veggies like broccoli, cauliflower, etc you might want to blanche them ahead of time or steam them, as stir-frying won't really get them tender.
Stir your ingredients in the wok and cook them for a few minutes. Then add your next round of veggies. Basically, start with the longest-cooking ingredients and add more based on cooking time, from longest to shortest, so that everything ends up cooked at about the same time. Once everything is pretty much cooked, add your sauce. This can be just about anything. My favorite is a blend of sesame oil, rice wine, soy sauce, brown sugar, ginger, and garlic. Toss your stir-fry with the sauce until coated. Cook for a minute longer so the sauce can sort of cook into the ingredients. Then serve the whole deal over some rice, cous cous, udon noodles, etc.
Really, though, there's a lot of room for error and for experimenting, so go nuts and just try what sounds good.