Hi Diana-
I baste my quilts on the floor too. And I mean floor--not carpet. My first step is to tape the backing to the floor using clear mailing tape. I tape a piece about 6" long at the center top, then smooth and tape the center bottom, then the same on the center of the sides. Next I smooth and do tape each of the corners. I go back and fill in with tape on the sides and top and bottom. I do not tape every inch all the way around. I just use pieces about 5-6" long and usually leave 5-6" in between each piece of tape too.
Then I lay my batting on top and smooth it. Then I add my quilt top and begin pinning.
I hope this helps you.