It really depends, if I can't keep up with the speed and power of a very hard kicker to evade, I try to deflect much of his force by countering during an exchange. Counter front kick to a rear leg body kick to divert a lot of power from his rotation.
If I am able, most of time I will just catch the leg after moving and pivoting away from the direct line of force.
Blocking with your arms is one of the worst things you can do against a hard kicker, face someone who does full contact striking from karate/muay thai, and they destroy your arms so you can't even punch let alone keep your guard up.
Driving your elbow into the side of their calf after a round/side kick is mean, but it's quite effective.
Lunging in and cutting off their hips from pivoting will reduce most of the power and you can go in for the shot to the face and unbalance them or knee their inside thigh of the kicking leg with your opposite leg is a very nasty technique, really painful.