go and buy a specific foot for the machine called different things on different brands ,... but basically could be ditch stitch foot or edging foot...anyway it has a piece of metal attached that you use to follow the ditch or edge of a piece of fabric....then set your needle to follow the metal guide or to a possition a specific distance from the guide and be consistant...go ask at your machine shop.
hope that helps
Mikany

I had problems with this too at first and I was told to watch carefully which "side" of the ditch I had ironed the 1/4" seam. That is what seems to make it hop. I finally decided that if I were going to stitch in the ditch I would iron the seams open and that seemed to fix the problelm. Hope this helps.;)

jrob and mikany just mentioned both of my ideas. Wish you luck.

Normally when you do a quilt you will turn your seam to the dark side. (It's the traditional way to do it) If you have done some basting or a lot of good pinning, your fabric should not slip so much. There is a great little foot that has a guide that rides in the ditch. If you don't have it, just go slow and exercise a lot of control. Some times if the seams in your blocks aren't perfect. It shows up now. Keep at it you may have a ribbon winning quilt.

I have that "ditch foot" the others were talking about, I like it a lot. Are you using a "walking foot"? That could help, too. Marji