Landing Boost can be performed with the "Landing Boost" tuning part, which is an Epic tuning part that can be obtained on all vehicles except Monowheel, equipped by ensuring the vehicle lands from an at least 1 second long jump with all its wheels touching the ground simultaneously. Successfully performing this move will be signified by a sudden "dash" forward of speed by your vehicle, as well as a discharge of sparks from the wheels and a distinctive sound. If you combine it with "Jump Shocks" and activate them at the right moment, it will give you a boost up and you can speed up your momentum for a longer time by perfectly performed jumps. Landing Boost can be used even after running out of fuel.
A visual example is included below: