For those who develop sore shoulders and backs from quilting while sitting down, you might mention that standing up helps. When I quilted on my domestic machine, I placed it on my cutting table. I could FMQ two or three times as long without back/shoulder pain and stiffness later.
Another thing that helps, especially if your machine is not sunk flat into a large table or desk, is to create a large styrofoam "surround" for your machine. This is easy to cut from a slab of styrofoam insulation. Cover it with inexpensive plastic. This makes a lightweight, large, flat, slippery surface for your quilt to rest on while you move it around. I particularly liked using this when quilting standing up with my machine on my cutting table.