I cant get down on the floor so have to do it in sections on my cutting table.
I clamp the backing around the edges with it as close to centered as I can eyeball.
You can use those large black clips but they are hard to open so I bought the white plastic clips for cutting tables.
Then I lay the batting and top on and clip them. Once it is pined I remove the clips and move the quilt over and reclip for the next section.
This works for me and dont have any folds.
My table is from Joanns and has two leaves that fold down for storage. It was $50 when I bought it years ago. Thay are more expensive now. It is only 36 in wide so do not do bed size quilt they get sent to the long armer.