Here's one I did with a bit of gridwork in it. I used the edge of the foot and chalk markings to keep a straight line. Measured the width of the section I wanted to grid; divided that by 4 or 5 and marked it.
http://www.quiltingboard.com/pictures-f5/year-finishing-ufos-t218989.html
In other quilts I skip over sections that aren't conducive to the gridding, and continue on the other side.
Jan in VA