we do chin tucks, side to sides, and ear to shoulders, 50 of each as part of our warm up
chin tucks - lie on your back keep your head slightly off the mat, then tuck your chin to your chest, then lay your head back but do not let it touch the ground. So it's like nodding "yes" without letting your head touch the mat.
side to sides - lie flat on your back, keep your head slightly off the mat, and take your head side to side as if shaking your head "No" to the left then to the right is 1 repitition
ear to shoulder - lie flat on your back, keep your head slightly off the mat, tilt your head to one side then the other, trying to touch your ear to your shoulder.
warning, these exercises are horrible, but will stack your neck and provide immense help in the guard and for bridging/sweeping.