If you're feeling tightness in the front of your thighs or hips, one of two muscle groups is probably to blame: The hip flexors or the quadriceps. Although the hip flexors are primarily responsible for hip flexion and the quadriceps are primarily responsible for knee extension, there's some overlap in their function and it's easiest to stretch the two muscle groups together.
Single-Leg Standing Stretch
Doing one-legged standing stretches saves you the trouble -- or sometimes, the struggle -- of getting up and down from the floor. It's also a way of multi-tasking, as you get to work on your balance as you're improving your flexibility.
Stand near a wall or chair you can hold onto for balance if need be. Bend your right leg and grab your right foot with your right hand. Keep your knees close together as you bend your knee and point it straight down as much as you can. Push your hip forward slightly until you feel the stretch really engage across your hip and down the front of your thigh. Repeat for the left leg.
If standing on one leg makes it hard for you to relax into the stretch -- or perhaps your quads are too tight to fully flex your knee -- dial it down a notch by doing a standing lunge instead. Take a big step forward with one leg, weight balanced evenly between your feet and both legs straight but not locked. Tuck your pelvis and push your hips forward slightly, bending your back knee a little to facilitate the motion. You should feel the stretch across your hip on the side of the back leg and, depending on how tight your muscles are, down into the front of your thigh as well.
Lie Down on the Job
If you want to relax a little more during your stretch, you can do a variation on the single-leg standing stretch while lying down. Roll onto your right side and then bend your left knee so you can grasp your left foot with your left hand. If you can't reach your foot, grab your pants leg or, better yet, wrap a towel or bandana around your foot and use that as a handle of sorts. Pull your foot toward your buttock on that side as you keep your knees as close together as possible. If you don't feel the stretch, push your hips forward slightly.
Aim to hold each stretch for at least 10 seconds. It feels so good to stretch tight quads and hip flexors that you might want to hold the stretch for longer -- that's fine, as long as you're stretching to the point of mild tension instead of pain. Don't bounce the stretch. While you're at it, make sure you repeat the stretches on both sides of your body.