First off, you need to land with your feet over your trucks. This will take practice - most skaters end up with their feet shuffled forwards or back. If you land with your feet over the trucks, the trucks and wheels will take most of your weight and your board should be OK.
Second, you need to bend your knees DEEP. This is the biggest problem I see. You need to BEND those KNEES! Bend them deep, to where you are almost sitting. When you watch a skate video, you should notice that the pros really bend their knees deeply when they land.
Bending your knees like this helps to absorb the shock of your landing, and protects both the board and you. I saw a large skater once who busted a board about one a week, and he thought it was because of his weight. It wasn't. He would land with his knees stiff, and so the only things that could happen was either the board had to break, or his legs had to. He should be happy the board was made of weaker stuff than he was!
the last thing to keep in mind is to try and keep your weight balanced. If you land with most of your weight on one foot, then that spot on your skateboard will take that much more shock. So try to keep your weight as equal between both feet as you can. I know that this isn't always possible - some tricks just push you more forwards or backwards, but at least try.
Follow these steps, and you should save more skateboards! But keep in mind, even the pros break boards. When they're filming for a video, they'll break a LOT of boards, often several in one day! Keep these points in mind though, and you should be as OK as you can be!
