Hi Emily ~ Neck Pull is a tough one! You'll find a link to a short video of me teaching Neck Pull to Meredith Rogers below. In the video, I try to offer helpful hints and suggestions. There is also an ongoing discussion on this very question in the "Instructors corner" section of the forums. The fact is it is one of those exercises that takes time and the willingness to not worry about it being perfect as you practice. Good Luck!
Emily - go to the beginner center and look for "a towel for low back tightness" exercise. Try implementing it with the neck pull and see if it helps you - it was an incredible breakthrough for me after loads of experimenting.