I have found a lot of women who seem to have a nice actually don't have that great of an ass. It only looks bigger purely by pelvic tilt and over arch in the lower spine. If a women puts on heels it accents this even more ( why girls in heels usually look better ). Majority of the population sit way way too much, sitting stretches the muscles in the glutes, and as you know stretching makes a muscle weaker. I like to start every session with a women with a set couple sets of supine bridges, holding the top position for 3 weeks and really making sure they squeeze through the glutes. and moving to a one leg variation as they get better. Every leg exercise they do make sure they finish with a nice squeeze through the glutes. Every exercise try and make sure the hamstring and glute are being squeezed and place less emphasis on the quads. So for example, when doing step ups focus on using the back of your leg to kinda pull your torso towards you instead of using the quad to press yourself up. ( the quad is coming along for the ride no matter what trust me ). When doing lunges the same deal, whether your doing walking lunges or standing in one position, make sure the ham and glute is pulling the body in position... its easier to do this with walking lunges. Honestly this is just how to perform these exercises correctly and is something that isn't emphasized enough... I hope the info helps.
