Ways of leveling alt jobs from 70 to 80 efficiently? ?

[Kokonji]

just do the highest level dungeon you could do...
combine them with food, squadron buff, and ask your fc officer to activate the battle exp buffs...

I completely agree with the person above, though I wanted to add...

I see people saying "do roulettes," so I wanted to point out that doing the lv50/60/70 roueltte gives less exp than just doing the most level-appropriate dungeon (or at least, I think it was the last time I checked; please correct me if I'm wrong). Skip it.

I usually just stick to the leveling roulette. I'm not sure which other roulettes are worth the time.

I believe dr alliance raid give decent amount of exp as well
with the current event of moogle tomes you'll have ridiculously high chance to get Crystal Tower series which is the easier and the faster of all other raids (and it also gives clusters if you lucky to get those adventurer in needs)

[ADarklore]

just do the highest level dungeon you could do...
combine them with food, squadron buff, and ask your fc officer to activate the battle exp buffs...

)

If you're talking about the Squadron Battle Manual, it does not stack with FC buff.