It all depends, not all conventional fighters throw their rights the same.
Option 1) If a fighter has a tendency to lean in too much after he throws his lead right, then an uppercut would be perfect.
- Just keep in mind, when you sense or see that lead right coming, time it and step back a lil bit and fire off whatever punch you see fit(usually an uppercut or a lead left straight of your own and just follow it up with whatever punch you see fit)
Option 2) Another one is simply duckin' under it, and firing off a left hook to the liver or shovel hooks. Ducking under his power hand is a bit dangerous though, then again, a mis-timed slip or bob is never good.
Option 3) Slip his right straight by stepping to your left and firing off a straight or hook of your own and just improvise from there.