This stretch/pose was made for runners, obviously. You're getting into the same position a sprinter would and stacking your knee over your ankle while letting your back knee rest on the ground while leaning forward. Too far forward will make it painful and too far back will take you into a different stretch. Keep your head looking forward, breathe, and relax. If your right leg's forward, you should really feel it in your left hip flexor. (repeat for the other side)
Modified Runners Lunge for Quad
Stay in Runners Lunge and distribute your weight between our back knee and front foot. Begin by lifting your back foot while keeping your knee on the ground. Stay here if you're really feeling the stretch in your quad. Start reaching back toward your foot, while maintaining balance, hold your foot and encourage your foot toward your back if you want to intensify the stretch. (repeat for the other side)
From runners lunge, rock your weight backwards as you lift up on your back knee. If your right leg's in front of you your right foot should lift up and your toes should point towards the sky.
You should be feeling this in your hamstrings at this point. To intensify the stretch, simply lean forward and if you're very flexible, work your way into full split. (repeat for the other side)
Standing IT Band Stretch
Start by standing with your feet about hip distance apart. Lean forward and place your right hand on the ground about two feet from your feet. At the same time, slightly bend your right leg and keep your left leg straight. This should encourage your body to open (or twist) to the left. To continue opening your torso, raise your left arm straight up and pull your shoulder blades together.
I like this stretch because I get a twist for my torso and an IT Band stretch. If your muscles and tendons are really tight (like mine) you'll also feel this stretch in your hamstring. (repeat for the other side)
With one foot behind and one foot in front, lean forward and try to get your nose to touch your knee while keeping your back heel on the ground. That's all there is to it with this one. This is great to loosen up those tight calves and you might even feel it a little bit in your hamstrings. (repeat for the other side)
Seated IT Band Stretch
Sit on down with both legs in front of you. Start off by grabbing the outside of your left foot with your right hand. Lift your leg and pull it across your body (to the right). As you're pulling your leg across your body, twist your torso to the left and place your left hand on the ground behind you for support. The closer you bring your leg to your body, the more you'll feel the stretch in your IT Band. (repeat for the other side)
Cow Face Pose
Get on your hands and knees, keeping your legs, knees, and feet together. Lift your right leg and cross it behind your left leg. Spread your legs and feet out wide while keeping your knees together.
Carefully sit down on your sit bones, go as slow and be as methodical as you need. Once you're on your sit bones, adjust yourself as need be, even if that means your knees pop up. Keep your feet split wide, knees stacked on top of one another, with your weight dispersed evenly on your sit bones.
If you do feel pain in your left knee, use your hands to roll your quad muscle to the left. You should feel this in your IT Band and hip flexors. If you're not feeling the stretch, begin to lean forward with the intention of trying to touch your head to your knees, until your start to feel the stretch. (repeat for the other side)
These are some of my favorite yoga stretches to do after running, never before I run. If you choose to try out these stretches, remember that you want to feel a good, relaxing, pain in your stretch. When the stretch starts bringing you to tears or profanity starts flying out of your mouth, you've gone too far. Take it back a notch or two and enjoy the stretch.
Disclaimer: I'm no yoga teacher, just a guy who runs, does yoga, and has found these yoga stretches help me out.