The microphone element should be positioned by the corner of your mouth (for some reason I always use the left-hand side of my mouth), about 1/2 inch from your mouth. I actually cheat. Because I have a mustache, I know that the microphone is positioned correctly if the foam windshield is just brushing the tips of my mustache hairs.

I recommend that before every dictation session, you squeeze the microphone element between your thought major finger with your thumb on the inside. The microphone element should be flat, and there should be a colored dot on the inside of the microphone element (where your thumb is). Then position the microphone element so that the back of your thumb touches the corner of your mouth.

Make sure that the microphone does not move. I check it a couple of times every session to make sure that is still positioned properly.