My first tip is to try quilting standing up. I find that I can quilt much longer this way without my shoulders and back stiffening up. I place my sewing machine on my cutting table and find that to be a very good height.
Second tip is to make an inexpensive styrofoam "surround" for the machine on the cutting table. There are some Youtube videos on how to do this:
http://www.youtube.com/watch?v=g14govA4pIM
http://www.youtube.com/watch?v=yAS25v3ZTk0
Third tip is to arrange a table or ironing board to the left of your quilting area to hold part of the quilt. This really helps spread the weight of the quilt.