It is important to understand the attack patterns and choose the correct response.
Some monsters’ attacks are simply a trap for certain moves from certain weapons. For example, if you stand near and evade to the left or evade towards or away from the first fireball, the subsequent fireballs will not hit you. If you stood about 2 rolls away from the Rathian and evade the first fireball to the left, you will get hit by the second fireball. If you evade to the right, you should still have enough time to evade again before the third fireball hits you (I have done this before), but it depends on how close you are to the monster.
As such, this is the pattern. If you don’t want to get hit, simply avoid doing the above.
I like to evade into the first fireball so as to avoid the other two fireballs easily, or I simply stand near to the head so that when I perform perfect evasion to my left on the first fireball, I still have invulnerability and will not get hit by the second fireball. I have stopped evading to my right since a long time ago when I realise it is a trap.
Similarly, if you get hit by Kulu-Ya-Ku while you’re using a heavy bowgun and you tried to roll forward to quickly recover from the attack, you will get hit by Kulu-Ya-Ku’s next attack before you can recover from your evasion. The solution is simple: simply don’t roll forward.