Tight hips can be caused by many different things including arthritis, muscles imbalance, strains, sprains, and alignment issues. These hip stretches should help.
You basically want to stretch out all the muscles around your hip to help relax the hip muscles. A knee to chest stretch stretches the low back and posterior hip muscles, a butterfly stretch stretches the groin and adductor muscles, a piriformis stretch stretches the piriformis and glutes, and a hip flexor stretch stretches all the hip flexor and anterior hip muscles.
Standing up, you can work the hip muscles swinging movements to help relax and decrease the tightness. Hip circles, hip abduction/adduction, and hip flexion/extension swings do a great job of working the hip muscles and relaxing them as well.