Summarize:

You might be able to prevent a fall by getting off the skateboard and running. Jump off your board by placing your back foot onto the ground in front of the skateboard, and following with your front foot. Begin running in the direction that you were traveling in and only stop the board once you have slowed down and regained control. Practice your running technique from a stationary skateboard first. Once you have got the hang of this, try running from a moving board, in a quiet space. Only try this at the skate park after lots of practice. Bailing is when you opt out of a trick before you get hurt. If you know that you're about to fall hard, you can try and stop the trick before it's too late, and jump off your board. Rather a bruised ego, than a bruised leg!   It is important to kick your board away when bailing, as you don't want to land back on your board and slip over. If you kick forward there is a greater chance that you will land back on the board, so always kick the board behind you by kicking your legs back. Bailing isn't good for your board deck, and it will cause scratches and chips. However, it is better to bail and chip your board, than to not bail and hurt yourself. If a fall is inevitable, you need to use all your limbs to soften the impact. It is important to keep your arms and legs loose so that they can absorb the shock of the fall.   If you stiffen your body, there is a greater chance of you breaking bones. Keep those limbs loose! Don't break falls by using only your outstretched arms. Wrist injuries are rife in skateboarders, and this is going to hurt or cause you to break your wrists. It's a good idea to wear knee-pads and if you are going to fall whilst on a ramp, always fall on your knees. This will cause you to slide down the ramp, and avoid serious injury. Rolling distributes the impact of a fall and prevents serious injury. Remember to shield your face with your arms and aim to land on your back or shoulders. Practice falling correctly on a soft surface before you hit the skate park. This way you'll be prepared for future falls and falling safely will become second nature to you.
Run-out to avoid falls. Bail out when you need to. Fall correctly. Break falls with your knees if you are skating on a ramp. Roll after a fall. Keep practicing your falls.