One thing I do that helps me keep my fabric going straight is put a strip of mole skin to the right of the needle on the plate at the 1/4" mark. I can keep the fabric butted up against that and I don't veer nearly as much. I tend to veer to the right (I think I push with my left hand a little) and my seam is a little fatter at the end. With the mole skin as a guide, it's not nearly as big a problem for me. I have to swap the mole skin out pretty often as it gets ragged looking, but it doesn't take a very big piece and it's not terribly expensive. I've seen people on tv use a thickness of painters tape also.