Position yourself to the edge of the gap with a last clean controlled hop
1° Lean forwards while crouching on the uni to pre-load your extension and tilt the uni in the direction of the move.
2° Unfold at the waist and thrust your free hand forwards , keep your ankles well flexed while compressing the tire.
3° Spring up with the knees and ankles pushing on both pedals, combining your extension and the rebound of the tire.
4° Take off by bouncing back from the tire compression, pull on the seat while flapping your hand down.
5° In air, swing the unicycle forwards by extending your legs in front of you and keeping the seat close to you.
6° If you have to land on the spot, make sure you land with equal weight on both pedals, to stall sharp, pedals parallel.
When landing on narrow surfaces, you can keep both feet firm to stop and bounce off or make a few correction hops before the next move. See the move in a video
Finding a direction
Gap jumps on a unicycle require a lot of commitment, as you don't kick in the pedals to roll off the edge, you get most of your forward momentum from body-movement, leaning forwards and tilting the uni in the direction of the move before a beefy compression like for a big side-hop. There isn't much way back, once you've pre-loaded the move, except pulling the seat out and landing on your feet. When jumping over big gaps, one way to avoid accidental rolling is to take-off and land at an angle (30 to 45°) with the direction of the jump. This will make stalling easier, as the landing friction won't force the wheel (and the pedals) into rotation.
Also, the angle will secure a better grip for the tire, and offer more rebound especially if you land on a sharp edge, because there is more surface to hit and bounce from than if you landed just on a tiny tire section.
Optimise your jumps by pushing in extension when the tire is bouncing back from compression. You'll get all the effect in one big acceleration up.
Swing your free arm up during your extension, and then down in one big arc towards the landing spot. This flapping action will help you swing the unicycle forwards and control your overall position in air, so that you land well balanced.
Rolling gaps: more flow in the move.
When jumping long distances or in drop-gaps where the landing impact can be harsher on your crank, it is better to roll off the landing point right after landing, to dissipate the shock into a rolling motion. Else, you'll end up stopping bluntly and maybe trashing your crank axle. Also, to get more flow and all the momentum needed to jump over big gaps, you can roll right up to the edge of the gap, instead of stopping and bouncing around until you take a decision. Basically, while you roll up to the edge of the obstacle, finish your pedal turn on your good foot to stall very quickly and stomp down firmly on both pedals. This builds up the equivalent of a compression-hop while your body keeps moving forwards, leaning into the extension when the uni is stalled.
Rolling or not rolling?
To make the most of the rolling hop, finish off the last pedal turn by accelerating the move and almost kicking in your good foot forward, but stomp with both feet and stall for maximum tire-compression when both pedals are reaching a level position. This will load the tire as if you had been bouncing on site, but with extra momentum forwards. Off course, your upper body is still flowing forwards and that tilts the uni towards the gap. At this stage, you have already crouched, and as the uni is tilting, you are ready to take your impulsion and jump. Try to synchronize the mini-kick with progressive crouching and bending at the waist to build up your impulsion. To land a rolling gap, damp the impact by pedalling off rather than stopping flat out (your crank will thank you for that). Always land with both crank arms aligned to the ground but quickly push on your good pedal to roll one or two turns. The speed at which you roll-off will determine your shock absorption (converting linear kinetic energy into a rotational kinetic energy). But keep control of that pedalling, else the unicycle will shoot away from you and you'll end up on your bum.