Try your walking foot on a practice swatch and make sure it works properly. You'll be able to tell by the fact that there won't be a pleat of extra fabric when you get to the end of a seam. :)
If you have to use a regular presser foot, try to use one that has the least amount of surface area touching the feed dogs. A vintage quilting foot is ideal - it's a very short foot. Then, adjust the pressure on the presser foot so that if you have your stitch length set to 10-12 stitches per inch, you get 10-12 stitches per inch on your quilt, and then ease off of that pressure very slightly. This helps keep the top from stretching quite so much.