When I lived in a house with wall-to-wall carpeting, I'd spread my quilt backing out on the carpeting and stretch it taut and square, pinning it to the rug every 5-6" all around with straight pins. It is possible to get it very tight. Then I'd smooth the batting out over this.
I would next stretch the quilt top, pinning its perimeter too to the rug; not stretch it out of shape, but stretch it so that the blocks and borders were straight and square, and the top lay flat and fairly taut. Once I was satisfied with the way the top lay, I would pin-baste it with 1" safety pins, spaced about 3" apart.
Now that I don't have the wall-to-wall anymore, I use painter's tape (blue or green) to stretch and hold the backing, and the quilt top, on a clean wood floor. The green tape holds a bit better than the blue. Again, be sure to get the backing perfectly smooth and taut. I use contractors' knee pads (bought at the hardware store) to spare my knees from the hard floor.
As long as the quilt back is very tight and flat before pinning, you shouldn't get any pleats or puckers in the back when you quilt. I always aim to get the backing a little tighter than the top; this way, if any excess fabric is going to bunch up, it will happen up top where I can see it before it becomes a problem.
Do use a Kwik Klip for the safety pins -- well worth the cost, once you see how quickly it closes pins... and how much better your fingers feel when you're done!
If I do accidentally get an unwanted pleat, I've found I can pick out the offending stitches, ease in the excess fabric "bubble" by basting down with water-soluble thread, and then re-quilt. Washing removes the basting stitches, and no one's the wiser!