Hip tightness is usually associated with muscles that cross the hips - 22 of them including hamstrings, glutes, and inner thigh muscles rather than the hip joint where the thigh bone (femur) meets your hip bone (pelvis). Compensation for this “hip tightness” can result in issues throughout the body. In particular, this compensation may be a contributor to lower back pain and knee pain.
Many yoga poses and Pilates exercises improve flexibility and hip mobility.
Front of the hip pose is a great stretch particularly for the rectus femoris (a quadriceps muscle) and the psoas muscle. Quadriceps attach below the knee so tight quadriceps can impact the knee as well as the hip. The psoas muscle is attached to the lumbar spine vertebrae, passes through the pelvis and is attached to the femur (thigh bone). Psoas tightness may cause issues with the lower back.
Start on your knees and step one foot forward. Do your best to get your front knee above your ankle. The other knee remains on the floor - you may wish to put some padding beneath it. See if you can get your front knee and front hip to 90 degrees. From there with your pelvis in a neutral position (ASIS/hip bones and the pubic bones all on the same plane) see if you can shift your pelvis forward taking your back hip into an extension. Hold for up to 1 minute and then repeat on the other side.