One key to strength training and building muscle is to make sure your muscles are being challenged. If you never change the stimuli (weight, reps, sets, exercises), your muscles will adapt and eventually stop growing and getting stronger. Because our glutes are the biggest muscle group in our body (our quadriceps and hamstrings also top that list), it's important to have an arsenal of ways to work them.
Squats are great for improving your lower-body strength, and one of my favorite variations is the pistol squat. It's a unilateral exercise (a single-leg movement) that will help strengthen both sides of your body equally (goodbye, imbalances), and it will improve your strength and stability.