Sometimes no matter how much I flatten the top, batting and back I seem to get a wrinkle or two when I do my own quilting. I like to do the quilting on the diagonal, I wonder if that is the problem?

I use these clamps I got at home depot and use my dining room table. I spray between layers and then pin. Never have any problems with wrinkles this way.

I tape the backing on the floor first(I have wood floors)then tape the batting and finally the top. I use painters tape but tape for posting packages works just as well. I then baste down the middle, across the middle and then diagonally from each corner. It may sound like a lot of preparation but it works well.

What kind of spray do you use?

I can't use my dining table. It's a family heirloom. :(

In addition to the above, are you using a walking foot? It will help.

I use 505, it is expensive, but lasts a long time.

My tip is to slightly stretch out the backing and fasten it down evenly around the edges before spraying and sandwiching the quilt.
Too tight or too loose on the backing in this step, and it will cause wrinkles no matter how well I spray or pin...

Do you hand or machine quilt? For machine quilting, it helps *lot* to heavily starch the backing fabric before layering. Starch stabilizes the fabric so it doesn't stretch while you are quilting.

I starch,, starch, and add a little more starch. Then I tape to the covering hung in the garage and spray glue. Then I add the batting, spray the back of the quilt top and pin the top row (pulling all the time) and smooth out over the batting. Once done, usually takes about 20 minutes or so, I add a few pins and start sewing with a walking foot (in the middle or there abouts). Hope this helps.