Here’s a simple drill to help you both strengthen and mobilize the hip rotator muscles, including:
- Hip internal rotators (rotate the thighs inward): piriformis (when hip is flexed), tensor fascia latae, glute medius and minimus
- Hip external rotators (rotate the thighs outward): glute maximus, piriformis (when hip is in neutral/extended), gemellus superior and inferior, obturator internus and externus and the quadratus femoris

Great drill to do in your warmup and/or in between sets of Bench Press.
Do anywhere from 6-12 reps per side or more!
And if you’ve got a lot of trouble doing this movement, then check out the Hip Flexibility Solution because if you don’t properly address your movement dysfunctions now, they’re only going to get worse.