The first 3 seconds is what matters most. That's where we capture 90% of the details of your expression. Be electric for 3 seconds. After that, just turn your head with roughly the same expression. You can relax. Just don't talk. Or laugh. You can do both when you're done.
Clear your face before your 3D scan. Remove glasses & earphones, and pull hair off & away from your face. We are going to remake you as a digital avatar. If you have hair, glasses, high collars, earphones, etc, in front of your beautiful face, we will assume that it is part of your natural bone structure and you will come out looking lumpy. (Which is fine with us if that's what you're going for... just saying.)
For best results, clear everything off your face so we can see that gorgeous mug of yours. You will choose a hairstyle later so don't worry about what your hair looks like during your scan.
Also, make sure your eyes and whole face are well lit. Avoid harsh bright lighting, and avoid lighting that casts shadows on your face - we want to see your whole mug. Incandescent and warmer white lights will give you a good healthy glow while LEDs are too blue and can make you look pale & icy, but maybe you want to look like a White Walker. That's up to you.
Here's a silly video that might help you out.