Hip flexibility or stability? Both are important and can help prevent issues down the road. Here is an excerpt from womenshealthmag on how to do a hip flexor stretch ( I also included a video !)
"Begin in a half-kneeling position with one knee on the floor and other leg in front with knee bent at 90 degrees and foot planted on the floor directly under knee. With core tight, chest high, and hips squared, let forward knee glide forward while slowly driving hips forward until you feel a stretch in the front of the hip."