Pages have been posted on how to give a guy a backrub, covering every angle of the subject. The flipside, however, is left mainly uncovered and maybe even tainted by the "backrub for a guy" nodes, since the processes are completely different.

That said, all of the muscle groups of the upper and lower back are the same between the sexes. It is wise to start with a soft rub of the entire back area, placing your fingers on her shoulders and rubbing the balls of your hands along the muscle located directly under it, towards her neck. When the balls of your hands reach her neck, move them downwards towards the base of her spine in a lightly pressured, wavelike fashion. (Sort of in-out-in-out.) When you reach the base of the spine (close to where the pants start,) move your hands apart, as if to squeeze the pressure out of that region. (If she sits for any part of the day, there will be a lot of stress in that area - we'll come back to it.)

At this point we return back to her neck and rub the muscles supporting it (on the lateral side of her neck, seperating sideways into her shoulders.) Be aware that these start at the hairline. The idea is always to move tension to the outside, where it dissipates into skin tissue.
By now you're well into it. With a little bit of practice you can feel out where the tensions lie and are able to rub them out. Just remember to use broad, evenly pressured strokes. A brief rundown of the major groups that attain tensions follows:

  • Neck Muscle - connects the head to shoulders, use the side of your thumb and the ball of your hand to rub from the top to the shoulders to the neckline.
  • Lower shoulder - runs above the shoulder blades, gently pull up and release
  • Outside shoulder - softly knead, as if you were trying to pull it out / lengthen it to the outside
  • Erector Spinae - This muscle runs along both sides of her spine, rub it down and out (wavelike motion, again.)
  • Back Base - The muscle mass where the belt lies, you can use a bit more force on this one. Use your flattened hands to rotate it outwards, away from the spine.

Thanks to JessicaPierce and icicle for complaining about not getting any good backrubs lately and inspiring this node =)