Hi there...Janet's suggestion about kneeling first makes a lot of sense (mainly since that is how we train our people as well
A few thoughts...
1. Kneel with your toes up
2. Stick out your right hand directly in front of you (assuming right hand roll here) with your thumb up as if to shake hands. Then turn thumb down and make a loosely closed fist. The top of the hand (NOT THE KNUCKLES) will be the first part of your body to touch the ground.
3. Allow your arm to bend with the elbow up in a very shallow curve.
4. Tuck your head so that you are looking through your belly button and out your...well...anyway
5. Straighten your left arm behind you and up until it locks into place as far as it can go behind you and beside your body (directly beside/straight don't move it behind your back or more to the open left side)
6. Straighten the left leg behind you so that you are pushing over the right knee. Your right hand is not yet touching the ground. Push your toes so that your weight goes even more over your right knee until you start to fall.
7. As you start to fall make sure your head is tucked in, that the front arm keeps that little curve, that the back arm doesn't move from that locked position behind you, that your back leg stays straight and reaches for the sky and that you are moving forward a little as well as down so that the edge of your hand (meaty part just up from your baby finger opposit the them...remember the loose fist) touches the ground first.
8. Once you start to fall you should roll from your hand down your curved arm across your shoulders and end up slapping with the hand that was extended behind you. Keep that back left leg as straight as you can and turn the ankle sideways so that the heel doesn't hit the ground. The other leg should be pulled up to kick yourself in the butt and you should end up balanced on that foot.
9. Don't try to get up right away....just bask in the pleasure of the huge circle you've just made
But if you do decide to stand up keep your head tucked until you are all the way up and just push up on that foot that is tucked under you to do so.
Then move up to standing and then jumping and then jumping over people
A few more important points...
1. Do this with someone who can do it. Watch them and see what they do...they probably won't do it exactly as I do it, but match as many of the points above with what you see.
2. The biggest problem is that people don't believe that that front arm can support them when its curved. So they straighten it and end up jamming their shoulder right into the mat. Hurts. Not fun. Sad. Pain. Have someone hold your neck as you do this so you can trust that even if you didn't have that arm they wouldn't let you get hurt.
3. Repeat 10,000 times and rinse...
It's also worth going back and just doing somersaults sometimes.
FWIW...I am 190cm (6'2") so I almost know where you are coming from. I always think that I am safer in the air and try and get high rather than going toward the ground, which seems the opposite of what you have been told. I figure that if I can get my shape right in the air then the landing will take care of itself.
Remember...grab someone to help you!