You have to know how to F/S 50-50 Before you try this trick. It's hard to learn but it's a good thing to know.
Come up to your target on a little angle. When you get pretty close Ollie up even out with the target. It better to start on something low. I find if you land your front truck first then let your back truck fall half a second later is the easiest way to do it. But if you land flat it looks better. If you can't get on well try practicing Ollieing backwards overtop of something like hockey sticks. Until you can Ollie backwards higher than your target. By Ollie back wards I mean Ollie and land on a different spot then you started. But move backwards in the air. Then try it. It should be easier. To come out you can just manual or make up some other moves like shove-it or 180.
Here is a way that you can learn this trick almost perfect in about half an hour. You should be pretty good at skating before you try this though. Take out a hockey stick or a broom or any kind of long stick and set it on the ground. Ride parallel to the stick and about 2 inches away from it. The first thing you have to be able to do is Ollie B/S Over it (Like Ollie side ways B/S over top). So when you first try this you will probably make it if not the probably in the next couple trys. But, you will land at an angle as if you did a F/S 180 without the whole spin. Ok now at least you know you can do that. The put your stick back into your house and move onto step two. Step two is being able to late B/S 90. It's not very hard, just Ollie up and on your way down stretch out you back leg to twist the board 90 degrees. Try this for about 5 minutes until you are good at it. Now you have all the skills you need to be able to B/S 50-50, this is what you do. Come up this time to your grinding target and pop an Ollie like you did in step one, where you go over top of the target but where your front over twists like a F/S 180. Then once you have done that do step two still in the air, just stretch out your back leg and twist a late 90 or so to land even on the target. This took me two trys before I could land and grind. There is one more thing. KEEP YOUR SHOULDERS IN LINE WITH YOUR BOARD! It works believe me, just keep those 3 things in mind when you are doing them, Shoulders in line with the board when you Ollie on, Step one; learn to Ollie over something B/S but you will probably end up turning your front (if you don't you should be able to do this trick). Also don't forget step 2; late 90 before you land. If you look really carefully at the pictures below you might be able to see what I am talking about. In the first picture the nose is about 20 degrees F/S and in picture 2 you can see all the weight is on the back of the board, on the back foot. This is one of the signs that you are doing a late B/S spin to even out. Picture 3 shows your on.
Click Here to View the Video – Gedas
Click Here to View the Sequence – Gedas