I prefer spray basting to create the quilt sandwich -- a lot faster than other methods and easier on my back.
I spread out a large flat sheet first to catch any overspray. Backing fabric is laid down, wrong side up. Backing fabric should be bigger all around than the top. I fold the batting in half or quarters to help center it on the backing, then smooth the batting over the backing fabric. I fold down the top half of the batting over the other half, spray the exposed backing fabric, then smooth the batting back over it. Do the same with the opposite side of the batting. Now the backing and batting are secured together. I do the same with the top, folding into quarters to help center it, smooth it out, fold back the top, spray, etc.
Backing and batting are always cut bigger than the top. How much bigger depends somewhat on the size of the quilt, but at least one inch all around and more commonly 2 inches.
If you search on spray basting in this forum, you will find other threads about it that may be helpful.