Start with your back knee on the floor and your pelvis over your back knee. Squeeze your legs as if to prevent your legs from sliding apart. Then release.
Get used to this action, then each time you release, slide your front leg forwards just a little bit. Then squeeze and halt.
Have chairs nearby (or blocks in your hands) so that you can catch yourself if you find yourself going too far.
I've tried a number of different leg actions while using my legs to control their own decent. I'd suggest you do the same. It will give you more experience with your body. And it'll help you figure out for your self which action is the most helpful.
For a while I focused on the inner thighs. For the front leg this meant pressing the inner thigh down. For the back leg I focused on pressing the inner thigh up. If you have trouble focusing on both legs at the same time, focus on one leg first and then the other.
You may also find it helpful to activate the side glutes.
Another action you can experiment with is pressing your back foot into the floor, as if trying to lift your back knee.
For the front leg you could try pulling your heel back when you contract, as if trying to stand from the splits. Or you can try pressing your heel down during the activate phases.
Generally I find the scariest part is just before my front calf touches the floor. If you can see that your calf is only a few inches off of the floor, see if you can resist the urge to put your hands on the floor.
When (or if) you do get your pelvis to the floor, you may find that it feels great but you also want to get out as quickly as possible.
As you get more and more used to "touching down" see if you can hold this position and experiment with slowly relaxing your legs and then re-activating them as it trying to squeeze out of splits. You could also experiment with bending your back knee, grabbing the foot and pressing it down to the outside of the thigh similarly to hero pose (but with the thigh pointing down instead of up.)
When working towards splits, keep your spine long, including your neck.
Once you start working on doing the hands free splits, you may find that its easier to maintain leg tension if you do something with your hands. Whatever you do with them, make them feel long. Express yourself with them. You may find that the same "expressive" evergy finds its way into your legs, or it takes your mind off of the fact that you are slowly sinking down to the floor (What The Facebook!)
Although it is easier to get into splits if you turn your back leg out, I'd suggest keeping the back knee pointing down for a deeper psoas stretch.
You can also experiment with pushing your back foot down into the floor, as if trying to lift your back knee. Keep your pelvis square to the front.
Once you are used to getting your pelvis to the floor, then experiment with turning the back leg out. Careful with the back knee. Do this slowly.
To help work towards side-to-side splits, focus on pressing the back leg side of your pelvis downwards.
I've made fists in my version of this pose. At the time it felt cool.
Remember, while working towards the splits, keep your spine and neck long. Most particularly engage the front of your cervical spine, behind the throat.
For this variation of splits you can press the back shin into the wall. To prevent your back shin and leg from rolling inwards you can reach a hand back and place it to the inside of the lifted foot.
If you aren't used to doing this leg stretching yoga pose, it may be a good idea to warm up with high lunge, low lunge and even hamstring stretches. You may also want to warm up your arms with arm supported yoga poses..
If you can mindfully use your arms to support the weight of your body, you can then relax your legs.
These were the only chairs I had handy!
Non-folding chairs are preferable!
Initally when working towards front-to-back-splits, use your arms to support your body. If you can't go low enough to get your hands to the floor, use chairs to either side of you.
Make sure that your chairs won't slip, and that they are stable (i.e. they won't slip, nor will they collapse or fold while you are using them.)
Make sure that your place your hands on the chairs in such a way that you don't cause the chairs to topple over and fall.
So that you can sink deeper while keeping your legs relaxed, bend your elbows. Or gradually reduce the height of whatever prop that you are using.
One way to help stabilize your legs in splits is to use friction as explained in the Frictional Muscle Control video. This video teaches you how to use friction in a variety of poses, including splits.