Wheelswapping

There are many versions of how to do this - back brake off, front brake off, both brakes off, both brakes on - so just go with what you prefer. Some say back brake off means you can "compress" the bike more and get more fork flex and so on, but personally, I prefer the more control of having both on. You can still compress the tyres and flex your bike to hell if you want, and the end result's the same, plus your back tyre stays where you want it if you're riding natural and you're doing this on sketchy terrain.

Get your front wheel up onto the top of the object. Hop around as much as necessary to get your balance. One of the key things to remember is to turn your bike so if you drew an imaginary line from the centre of one pedal to the centre of the other (or "center" for the non-UK people ), it'd run parallel to the wall, e.g.:

This means the bike is as close to the wall as possible, and thus easier to get up. Think about it like how you do an "American" bunnyhop instead of lifting two wheels at a time :)

Anyways, you're now in the correct position, pedals level, close to the wall. Now, keeping your weight firmly above the headtube/front wheel of the bike, crouch down to preload.

Things to note: 'cos I'm a fatty fat fat fat, my tyre's compressed. This is all good. Equally, my arms are bent, so I can spring up as far as possible. This isn't like a lot of trials stuff which is all balance and technique, this is just brute force. You're hoping to send the bike up there just using your body weight, so really crouch down - bend your legs and arms. As you do it though, like I said, keep your weight over the edge of the wall/front of bike. Leaning back = nono.

Spring up. As you do so, just lift the bike straight up. You're not throwing the bike across or anything, you are just focusing on lifting the bike straight up. The way that you get the bike across and onto the wall is that as you're lifting the bike and your own body by throwing yourself up in the air and jumping with the bike, you throw the bars forwards, and tuck the back tyre up underneath you on the wall. This means all your efforts go into getting the bike forward for max height, and that you also still get the bike up there without nailing the back tyre into the face of the wall or anything. In that pic above, the bike is already lifted up level with the wall, so all I have to do is throw it forwards. If it helps you get your head around it, you should aim to end up as though you've just backwheeled the wall, that same sort of crouch/tuck position.

And there you go. You end up as if you've just been backwheeling, so just deal with it in the same way. Try and raise your body up asap, and get the bike up on the back wheel and in control. Alternatively, just let the front end drop and land it to two wheels.