If you make sure your quilt is secure and will not warp or twist as you sew, it is unnecessary to stitch in the ditch. A few basting stitches done down and across the quilt in a large stitch can help if you don't spray glue your quilt. I use the thread that dissolves in the top and ordinary thread in the bottom for this purpose as you only have to wash the quilt to get rid of it. Change your thread to start quilting and quilt all around the outside edge and gradually work into the middle. For machine quilting, you will have less problem with puckers.
Always practise for about 10-15 minutes on a small quilt sandwich to make sure there are no tension problems and that you get into the rhythm first.