I wind a couple of full strokes with the lever that leaves the backing paper mark short of the arrows in the camera. I then use my thumbs on the edge of the take up spool to wind some more film onto the spool to line up the marks. Not sure if this puts stress on the mechanism but so far has not caused any problems and always get the full 12 frames (except for the severely under-exposed shots of the inside of the lens cap! I don't feel so bad with the other admissions in this post)
I must thank Ailsa - it was her positive comments on the M6 in one of her editorials that led me to get a used camera and I am glad I did as it really suits my working style. I really enjoy using this camera!