At the sewing machine, keep your feet flat on the floor with your knees bent at a 90 degree angle. Using an adjustable chair is recommended. Again, find the height where your arms are also comfortably bent at 90 degree angle. Your wrists should then be able to rest on the cabinet or table.

Center your body in front of the needle.
Many people align themselves at the machine's center, which can distort your vision, as well as create unnecessary strain on your shoulders and back. The hand/eye coordination required for machine quilting is much easier if you are centered with the needle.  

Be sure to have adequate space to the left and behind your sewing machine to support the weight of your quilt. If you try to support the weight of the quilt with your arms while moving it under the needle, you will strain your muscles. If your sewing cabinet or work table does not have sufficient space, you can push additional tables up against them. Try to keep these as close to the same height as your work surface as possible.

Do not push yourself right up against the sewing machine. Allow approximately 5 to 6 inches space between your body and the sewing machine. Rest your forearms on the table as you stitch. This relaxes your hands, allowing you to freely move the quilt under the needle.

Sit up straight, aligning your head, shoulders and hips. If you lean into your work, you will affect your neck muscles, causing stiffness. You can also affect the nerves that run down to your wrists and hands, resulting in that 'gone-to-sleep' feeling. This feeling is actually a warning that the nerves are compromised.