the essence of bike trials
Trials riding is all about climbing on any kind of obstacles like a mighty goat. Climbing is one of these moves where you are more likely to smash the bike than yourself (especially the crank set). Walls and concrete kerbs are rather unforgiving for the chain-rings (try to practice on wood logs or heavy duty palets). Start easy and build it up.

8 climbing techniques for all kinds of situations

Using the bunny hop approach at any speed (raw street style). Rolling over the obstacle, a smooth quiet move. In one hop sideways, to bring both wheels on the same level. With a pedal hop, using the combined roll-over and pedal hop techniques (for low obstacles). From a static balanced position with the front wheel already onto the obstacle (for accurate positioning in time trials). Sideways, with a rear wheel hop, when there is no room for both wheels and it is too high for using the static hop technique. Banging or tapping the front wheel on the upper edge of the obstacle (for higher stuff where rolling over or the bunny hop are not possible) Hooking the crank (or bash plate) onto the obstacle, by landing a slow bunny hop or a pedal hop (that way you climb in two steps, but you need a good crank protection). Hooking the front wheel to an edge, to pull yourself up over huge obstacles (a two-step move, for the pros).

What pressure for the tires? It depends on the ground and the sharpness of the edges you climb on. The sharper the edge, the more inflated you want the tires so that you don't get a double pinch flat when banging the back wheel on it (the unfamous snake bite, rim rails pinching the tube against an edge). For round blunt obstacles like wood logs, less pressure gives extra gripping because the tire can litteraly grab the edges and shapes. less pressure also gives extra bouncing for landing, and is more comfortable. Fat tires (2.5" or wider) are the best, and allow a lower pression than thin tires, so more comfort and more grip.