Using a webcam to achieve good facial motion can be tricky. What you want to do is get even lighting on your face first, then you do want your face to be close enough to the camera so that your face should be taking up the majority of the screen. The closer your face is, the better the solver will be able to track your expressions.
If you are not using the head/neck rotation, try to not move your head a lot. If you notice you are doing something like moving your head alot and it is throwing the solver off (those lines around your eyes, nose, brows and mouth after you calibrate) the cleaner and smoother data will be the end result.