First of all, thank you Evette for sending us this beautiful Standing Separate Leg Stretching picture! This is such a great posture. It has tremendous benefits, including stretching and strengthening the sciatic nerve and tendons in the legs, promoting proper functioning of the abdominal organs and intestines, and improving strength and flexibility in the thighs, calves, pelvis, ankles, hips, and last five vertebrae of the spine.
When starting to bend forward in this posture, make sure to look straight ahead (NOT at the floor) with your chin lifted for as long as you can or until you "see your own moon rising" in the mirror. This will help to keep your back straight.
If you're a new beginner and still quite stiff, letting your spine lengthen by just hanging upside down will do wonders.
If you have trouble grabbing your feet, try grabbing the backs of your calves or your ankles, trying to pull your forehead closer to the floor. You can also try moving your feet in or out, more or less, and then trying to grab your feet, even if it is just the tip of your finger under your foot. You can always at first open your legs more and more, to get your hands on the floor in front of you to get your legs stretching.
Suck the belly in and stretch the sit bones up toward the ceiling while pulling and stretching the upper body down. The gaze is on the floor, centered between the feet but the neck should remain relaxed.
Keep your weight forward in your toes without lifting your heels off the ground. The goal is to touch your forehead on the ground between your heels, so you want to work on keeping a straight spine.
If you are having trouble, try relaxing and releasing the buttock more. To fully stretch the hamstrings, you must engage the quadriceps and lock the knees.
If your forehead is not touching the ground in between your feet, widen your stance a little. If it's touching the ground easily, challenge yourself bringing your feet closer together.