It is very important to have the same size thread on the top and bottom. Same brand if possible. But I avoid big contrasts in backing fabric. Learned my less with the first quilt I ever quilted.

Oh, you Sharpies people! I've used permanent marker on a favorite black blouse that had a couple of discolored spots. Fun for decorating fingernails, too.:D

Are you using the plate with the single hole and not the one for zigzag? It seems I read recently that that can help.

recently I have been using thermore batting, because I like its warmth and ease of handling. I have found that I can generally quilt with 2 entirely different colors without a problem, something I have never bet with other bats.