Mise en place is a French term... but don't hold that against it. It's a great thing for cooks of all levels to embrace...
Read your recipe... arrange all of the ingredients you need within reach... and it's a really good idea to measure out exact amounts into small bowls or containers. If you do this, you're not only more familiar with the recipe (because you had to read it again to measure things out), but you can add things at the right time without wasting the time searching for one ingredient. And while I'd recommend this for every recipe, I think it's an absolute requirement for stir-fry...
When you have your wok screaming hot, you can't stop to search or measure!