The first thing I do when I am quilting a large quilt is to anchor it somehow in a grid.
Many times there are lines to stitch in the ditch to anchor a quilt. Stitching in the ditch is stitching right next to the seam allowance in the ditch created when you press the seam in one direction. So it is important to make sure that you press seams in one direction. If you have seams that some how get crossed when stitched, you should go back and pick out the stitches and restitch the seam crossings.
When I stitch in the ditch I start in the center and work out to the edge. I use a walking foot on my machine and I adjust the tension of the top presser foot. Not all machines will let you adjust the tension but my Janome has a knob on the top left of the machine that loosens the presser foot tension.
When I did this baby quilt that measures 35” x 50” I stitched in the ditch down each line between the seams to anchor the whole quilt. Once it was all anchored I went back and stippled the top of the quilt with yellow thread on the top and on the bottom. I didn’t know what the sex of this baby was that was receiving the quilt, so I picked a neutral yellow.
My Woods is a 70” x 90” quilt. The first thing I did was to stitch in the ditch down the long stems of the trees and then around the branches, and the outside of the brown. After that I quilted all the elements inside the brown area. Then I quilted the first border and stitched in the ditch around it and finally I quilted the outside border.