Anything that helps to open the hip flexors and lengthen the leg muscles. For hip flexors: butterfly stretch, stacking one leg over the other in cross cross apple sauce, lunges, straddle, leg lifts in straddle position. All of these help to strengthen the hip flexors. Also bands help a lot! Now lengthening stretches come from a lot of the back of the leg. The backs of your legs can be very sensitive so it’s important to not strain the legs. Any pose where you are standing/sitting and reaching for your feet helps to lengthen.
Hip flexors are almost as important as your core muscles and back muscles for all major movements. For the splits however, I would concentrate on streatching my hamstrings, calf muscles, and glutes first. Also, plenty of squats, to loosen up the hip and groin muscles so you do not pull them in an attempt to do the splits!
I believe yoga stretches has some answers to your question: (remember breathing and holding each of the poses at least 30 seconds) Fırst warm up with Frog Pose then continue with Cobblers pose, possum(to open up inner thighs), then do lunge(to open hip plexer)then bring yourself to the advanced lizard pose..ouch it will hurt:) can go in to pigeon pose from there. Then pyramid pose to stretch your hamstrings. Then go to hamstring stretch. From here you can try to go in to splits. Can I do it:) ha ha. Not yettttt!!!!But believe me I used to and now I am trying.
It’s good to just try to decrease the distance you are from the floor when you do the splits, start little by little. Keeping a 90 degree angle at your inner thighs, sitting, legs stretched out on the floor, try to touch your toes and keep increasing the angle at which you are keeping your legs every time you get comfortable. Remember to warm up before stretching or you could stretch your muscles too much and it could cause injuries.
The best stretches include the straddle stretch and leaning forward on both legs for a minute each and then leaning forward for a minute. Also doing various lunges daily. It is also beneficial to try attempting the splits and see were it hurts and focus on those areas or stretching
The usual touching your toes. Remember to relax your muscles when stretching! Stretching isn’t like working out in the gym. The most important thing is to be patient. You won’t be able to see much progress for the first two weeks. But the results will come when you least expect it! Take care~