Hi - I am also pre-op and doing some physical therapy which they say will make post-op easier...! My physical therapist is familiar with resurfacing, which allows me to believe her about the post-op. I should probably state "I am not a licensed body work professional" in any way, and I hope it's ok for me to just describe what they've told me to do.
Like moe said, strengthening the muscles around the butt and hips. They've got me doing "clamshells" which I've heard talked about here: lay on your side, knees bent, and open the knees, keeping feet together. Do this without moving your hips back or forth, try to keep them still using abdominals, so that the gluteus medius (muscle on the side of your butt) does the work. I'm doing 2 sets of 15 each side. Twice a day if I can, which honestly only happens on the weekend.
Another one is the "bridge": lay on your back, arms straight by sides, knees bent, feet flat on the floor. Lift your hips/butt up, squeezing your glutes, push as far as you can, (I try to imagine I'm stretching my hip flexors on the front of my hips). For additional challenge, these can be done using only your heels (works the hamstring harder), or only with one foot (makes the hamstring cramp - oh, sorry, it works it harder as well as kicking in all the core muscles used for balance), or with your feet on an exercise ball (again with the core muscles for balance). Again 2 sets of 15 - I try to do at least one set with one of the challenges.
Also walking sideways with an exercise band around my legs, wall squats, stretching hip flexors and quads....