I've only done a few quilts, but like others have stated, since I've started taping my backing down, I've had better results. I use masking tape on all four sides of the backing, taping one side down then pulling the fabric taut and taping the opposite side down. Then I move to the sides and pull each side taut before taping down. Then I lay the batting and smooth starting from the center. I then lay the top on the bottom layers and once again smooth from the center. I haven't tried taping each layer, but did have that recommended to me. I have used both pins and spray basting and had no troubles since I started this way. Before when I just hand-smoothed the layers, I did have puckering.
Thanks for mentioning that donated quilts shouldn't have spray basting. I never thought of that and this is something I really want to start participating in.
Good luck!! You'll get it!