Biketrials pedal hop Sideways with a rear hop
For this technique, you should know first how to hop on the back wheel. Then from this position, you can do pretty much the same move as in a pedal hop, except that you must concentrate the impulsion upwards, instead of going forwards. This is also exactly the same move as in the sideways climbing technique, except that you start with the front wheel already lifted.

When there is no room to start with both wheels on the ground.
1° Balancing on the back wheel (brakes on), lower the front wheel to gain some impulsion and torque for the pedal kick. 2° Give a strong pedal kick while pulling a full extension upwards, both legs and arms extended, moving up with the front wheel. 3° Then pull up the bike with you by folding the arms and knees. Apply full brakes as soon as the rear wheel touches the edge.
See the move in a slow-motion video or in this one in a rocky section.

video
Joe using the bouncing effect
Starting already in balance on the rear wheel can give you more power for the pedal kick, especially if you amplify the bouncing effect of low pressure tires by crouching down rapidly before the pedal kick. If landing only on the rear wheel, either make sure that you have very good balance, or that you will have some kind of support for the front wheel, onto another edge. video
Power pedal kick by Olly
(slow-motion)
Else try to land both wheels at the same time to ensure a good grip. Note that landing the front wheel first will give you extra support to lift further the rear wheel.
video
Nico pulling on the bars
At the beginning, it is easier to climb with a slight angle, instead of parallel to the step. Start learning on a street kerb, and then on just everything. Stairways are excellent and the safest way to practice this technique. Also you can make it more difficult by climbing one step after the other on the rear wheel, without resting the front wheel. video
Cesar Cañas at a demo
video
on irregular blocks
Variations
Also try this technique on your wrong side (with your good pedal on the side of the step to climb). It is easier than you think, and you will learn more easily how to land the front wheel first for smooth climbing. On your wrong side, you can use the front wheel to grab an edge, even if the rear wheel doesn't reach the final height, and hook the edge with the bash plate or crank protection.
video
in natural biketrials

At a Pro level: pushing the move further
Most top riders use the front wheel as a guide for the whole bike lo land on narrow of very precise areas. Also, using the front wheel helps secure the landing and adds extra support to further lift the rear wheel, allowing to position the bike even before the rear wheel gets onto the obstacle.
video
Cesar climbing the odd side to front-wheel
video
Ben Savage aims his front wheel onto a beam.