Stack up mats or a resi behind the vault then go to your back keep doing it until you are like almost flipping upside down. Then just flip into the pit with a spot and stuff. Or you can try flipping on to like high mats then it will be much easier when you do it like on normal matting.
If you have pits... I would have to say just throw it assuming that you have good timers. The yurchenko is a mental thing. Actually I have a couple of 3rd graders throwing them into our pits and my 12 year old sister has competed them for 2 years.
Sometimes you just have to get out of your comfort zone.
As others have said--stack up mats nice and high behind the table and work on timers to your back; go for it into the pit either with or without spot if your timers are good; and don't be afraid to go for it--once you start the flip stick with it! They're really not a hard vault once you get the courage to go. Good luck and have fun!
Last time I did a yurchenko, last week, I rolled my ankle. But guess what, I didn't roll it doing the yurchenko, but rather jumping off the mat. Yeah, lol. At our gym, we stack up a whole bunch of 8 inchers on top or a resi, our vaulting table. Then we do the round-off back and try to land on our backs to simulate the flip. Also doing whips onto your back works too. Just remember that on the whip, you are going much faster than what you would on the table.
Like everyone said before me... 1) Stack soft mats up behind the vault and go to your back. This will help your rotation.
2) Stack hard mats up to the level of the vault or slightly lower. Make sure the mat is not very long. Put a mat behind the hard mat, like an 8" to land on. Do your yurchenko timer and land (well, punch) off the hard mat and do a back tuck off and land on the 8". The goal is to punch immediately when your feet hit. The timing off this is slightly different than an actually yurchenko, but it teaches you to get your arms up and your actually doing A flip somewhere after you go.
3) I believe that Tumbl Trak stops making these, but if your gym previously purchased one (or go to an open gym by your house), use it! It is a "vault table" that is portable and can be put on anything. It is a trampoline underneath the suede. Put it on the edge of a floor and an open it. Roundoff, yurchenko on, and flip off! Get a spot if necessary, but it probably won't be.
4) Lower your vault table. When you get more comfortable with these take them to a real vault landing, but at first go into a pit. Put the front of the board onto the "U-mat" (it goes around the board during yurchenkos). Stack a panel mat on top of that, and then one on top of that that leans against the horse. (This drill taught me how to twist, so it should teach you how to flip...unless you've already done tsuks.) Do a normal run, hurdle onto the panel mat, half on cartwheel onto the table, and flip off. This should teach you to block. Some people do it off a cheese, however that is more for a tsuk, if that is all you have, it is better than nothing, though.
5.) Final step before going by yourself, get a spot!!! Go into open pit foam. If you need to, put a sting mat on the vault. If you don't have a pit, go to an open gym or set up a private with a spot and the necessary equipment. Be confident and you can do it!