A good tip is if you find yourself in the middle of his zigzag pouncing trajectory, roll. It can save you.
When he tailwhips, if you find yourself in his face, roll under him. If you're on the side he's whipping, roll right when the tail is about to hit. This last part takes practise due to MHFU's mid-roll invulnerability being absurdly tiny unless you do it right after getting up from an attack that sent you to the ground.
Sonic bombs may help in a pinch. If you manage to make it explode while he's in the "power stance" (as dubbed by ScienceJesus), he'll collapse as if you made him fall from hitting his back legs. If it hits mid-pounce, he'll stagger, but get stopped dead. After either of those happen, he'll instantly go into Rage Mode.
The last option of course is sleep-bombing. I like to use Requiem Spear for that, given its neat sharpness and good enough Sleep attribute. Combine that with charging and Nargacuga being long and low to the ground... BOOM.