This is a great point, outside the physical training of having a fast kick. A fast kick can be that you kick before they have the opportunity to recognize you are kicking. Determine any telegraphing you may be doing when kicking. Cover kick execution, someone of my most used combination: jab, cross, push kick turning/round kick, push kick. fake/feint: feint jab - push kick fake low kick - push kick fake jumping front kick, front kick. timing the front kick to attack on their attack to intercept, learning to read their initializing movements. I used to drill this frequently: start with attacked coming with a lunge punch - front leg push kick/teep drill this static, then move to more live drill moving around then work the same as static drill with the attack not lunging, but with a cross, or an over hand punch. progress to a live drill with moving around. This is a great counter to make your front kick appear fast when it may be an average speed kick, just executing before they register it.