4) If you have one of the newer machines with the wider 9mm feed dogs, your fabric may not be getting fed into the machine straight because the foot being used is not fully covering the feed dogs. Ask your dealer about the foot required. For the newer Berninas it would be the 97D
I agree with QuiltE. If your machine has the option to set the needle over, you will notice that the edge of the fabric is fed directly over the feed dogs. It took me a long time to figure this out. I couldn't understand why anyone would mess with moving the needle or changing the foot just to sew a 1/4 inch seam. With these adjustments, my machine "pulls" in the fabric beginning to end straight and even. Good luck.