A few things that I have found that really help avoid puckering during the quilting stage are:
- iron the quilt top and backing well, and get the wrinkles out of the batting before spray baste, then take the time to really smooth out all 3 layers with your hands (gently)
- start quilting in the center of the quilt, working your way towards the outside
- check the back of the quilt frequently to make sure all 3 layers are smooth