First, I mark the centers of the sides of backing, batting and top. I also mark the CENTERS of backing and batting.
I spray baste. In good weather, DH puts saw horses outside & tops them with plywood or masonite. (In other weather, we do it in the living room) I put a sheet on top of that, then the quilt bottom. I use those big office clips to hold them taut - but not TOO taut- and I line up my centering marks. Then I spray the backing (never the batting - it can melt) a little at a time and press the batting on it. When that's done, I spread the top over the batting, matching the centering marks again, smoothing it with a yardstick, and I do a final check on the centering marks. Then I spray a little at a time, this time on the BACK of the TOP.
It takes about 15 minutes total for a twin size quilt, a little longer for a double. A large quilt will be much larger than the plywood or masonite, and I certainly couldn't reach the center if it WAS larger anyway! So I do the center first, then the sides, carefully folding up the sides, so they don't catch & tear on the edges of the wood.