and cook your chicken until it's just about fully cooked all the way through (depending on the size pieces of chicken and how hot your fire is, it should take about 2 - 3 minutes). If it starts to get dry, add just a tiny splash of water.
Add 1 teaspoon of oyster sauce, ½ teaspoon light soy sauce, ½ teaspoon sugar, and finally a splash of dark soy sauce. Keep stir frying for about another 30 seconds.
Grab a handful of holy basil, toss it into the pan, fold it into the chicken, and then immediately turn off the heat (if you're using an electric stove, you'll want to remove the pan from the burner). The holy basil really only needs to cook for about 5 seconds, and it will continue to wilt and cook from the existing heat of the chicken. This step is important because if you cook the basil for too long, it loses some of its glorious flavor and gets slightly chewy.
Notes
Make sure your rice is cooked and ready to be served before you start cooking... believe me on this one, because there's nothing more disappointing than finishing a pan of pad kra pao gai (ผัดกระเพราไก่) only to realize your rice isn't cooked yet!
Remember that the ingredients listed here are just a guide - they are the amounts I used - but you should really taste test all the Thai food you cook, and make it according to the way you like it!