For front to back splits, you can 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.
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.
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.
Note that this variation of splits could be thought of as bent knee hip flexor stretch (for the back leg.)