first of all this assumes you know how to draw humans. if you are trying to learn how to draw turians before humans, stop. there are plenty of tutorials out there that will teach you how to draw. this is just for these weird aliens.
I kept this as simple as I could, more down to the construction of their anatomy, rather than detail. doing your own gesture drawings (the third image) will help you familiarize yourself with how their bodies can pose.
I received requests for geth and krogan deconstructions too, so those are on the way!