I'm actually not sure what the exercises themselves are called, so I apologize beforehand if this is a little awkward.

I use some resistance bands for this purpose. They're fairly cheap on Amazon and work fairly well. The exercises are as follows

1. Lay on side with band near the knees on upper leg. Upper leg at 45 degree angle with waist, lower leg at 90 degree angle with upper. I then separate my legs. I do both legs
2. I stand up with band in same place. I then kick laterally as far as I comfortably can. I do both legs as well though I'm careful with my left one due to injuries.
3. I then get on all fours with the band, again, in the same place. I kick outward with one leg and return it. I do both legs here
4. In same position, I instead kick backward and straighten the leg. Both legs once more

I do about 20 reps each leg on each exercise with the heaviest band, so that may be why the progress is so fast. I couple them with my physical therapy exercises that I have to do for surgery. I do 2 days on, 1 day off so the muscle can recover.

Also, if anybody who knows better than I can suggest more exercises, please do. I want to have hips.

Oh, I also am starting up a regimen with my Total Gym here soon with a ton of exercises with that. Just gotta find space to set it up again. Has a ton of leg, hips, and ass exercises that I want to take advantage of as well. My set even came with a workout routine in the box perfect for this purpose. So hopefully that does even more.