When stitching in the ditch I use a larger stitch size, usually 3.5 or 4. First I make a little sample quilt with some scraps, about 4" x 12", to check out stitch size and also thread color before I begin quilting. I find that the larger stitch doesn't pucker the fabric.
I leave thread tails where I begin stitching and where I end stitching. I later go back and bring front threads to the back, tie the front and back threads together and bury them in the quilt sandwhich. This is a pain in the butt but I do it because I tried beginning and ending with 0 stitch length but it doesn't always look as nice as I would like it to.
My Pfaff has a built in walking foot so that helps a lot.
May in Jersey