Biketrials riding techniques Frontaly from a pedal kick
For this proper biketrials technique, you should know first how to hop on the back wheel, staying in balance on the edge of a kerb, and also how to pedal kick or you won't be able to decide when you are ready.

Dropping Off from a pedal kick or just releasing the rear brakes
1° Balancing on the back wheel, adjust your tire on the edge of the wall / kerb with a few hops. 2° Like for the pedal kick, lower the front wheel to the horizontal before you pedal off the edge. 3° Release the rear brakes and give a slight stroke in the pedal to get off the wall. Let the rear wheel drop first.
See the move in a video. Also see the physics of landing.

Minimising the drop off height
Once your rear wheel is well positioned, if you are jumping from high, make sure you lower the front wheel and crouch on the bike as low as possible before releasing the rear brake. Then once in the air, you can fully extend the legs again (with no impulsion but just following the bike down to reach the ground sooner). This move will actually reduce the total drop off height (compared to a high standing position with the front wheel lifted). Joe makes a perfect move on his mod (such an overkill for that step that as soon as he extends the legs, he reaches the ground). For the landing, rear brakes "on". Damp the impact progressively by leaning your body backward. The higher the drop off, the flatter you'll end on your bike. When the front wheel touches, most of the impact should already be absorbed by your legs and arms. The front wheel shouldn't bang on the ground (a wrist breaker).
video
Joe crouching before the drop.

video
combined drop off/pedal hop.
Landing smooth?
Let the back wheel hit the ground first, with the rear brakes "on" to gain extra damping power. Using the rear brakes will prevent you from slamming the ground with your back (not so healthy). Use the spring of your legs to absorb most of the impact.
video
Precision landing by Ramiro.
video
dropping off from public buildings.
In the air stabilise the bike aligned with your body, otherwise you're likely to be ejected sideways on impact with the ground. then lower the font wheel to the ground by extending the arms. The next step is to drop off from a natural wheeling. video
Landing in a slope.
If you have enough space for two pedal strokes, start on the goofy pedal lifting the front wheel, and the next pedal stroke (with the good pedal) should send you off the wall. Also you can try out some other stylish techniques like the front turn or the 180° twist.