I have had hip problems in the past.. turns out it was caused by a leg length discrepancy. Doc told me to put extra insoles in the shoe of my shorter leg, and wham! Problem fixed. I also do some hip-specific stretches. The first is for the IT band (another chronic problem for me). Cross one foot in front of the other, and then stick your hip out on the side with the foot behind the other one. So, in other words, to stretch your left hip, cross your right foot in front of your left, and stick your hip out to the left. Also, the classic hamstring stretch where you place your leg on an elevated surface, like a table, and bend at the waist is good to promote hip flexibility.