Things that help prevent this are: (1) heavily starching the binding fabric before cutting strips, (2) cutting binding strips on the straight-grain instead of the cross-grain or bias, (3) placing binding on top while sewing, (4) using a walking foot.
I also do something most quilters don't. When I square up, I mark the square with a permanent Sharpie pen instead of cutting. I use the line as my "virtual" edge when sewing on binding, and cut the quilt only after I have sewed the binding on. (Be *very* careful when cutting the corners, as you do not want to cut any of the binding that is there.) In my experience, this helps stabilize the quilt edge while attaching binding.