Majority of the time I get on in the evenings. So, I leave whatever make up I had on from earlier on in the day. Then, I add more to it: darker eyebrows, heavier mascara, overboard on the contouring<<(this isn't obvious on cam, it looks quite nice in my experience.)
However, the biggest portion of my prep time consists of heavy breathing,sweaty palms, mini panic attacks,and checking my webcam to see what I look like from the cam's perspective. All of which is a part of the mental mind-fuck I go through when convincing myself to click "Broadcast Webcam." Once the conversations gets rolling, I calm down, let my walls down, and just be myself.
I don't know if you drink, smoke, or 420. I don't do any of the above, but if I did, I think it would help take the edge off.