Mana Prism collecting

Events just wait for nerofest and other big events

That's pretty much it. You can also sell off the fires of wisdom you get, since it's more efficient to use blazes of wisdom in leveling up your servants anyway (with fires of wisdom being more efficient if you only need one to hit the level limit). I suppose if you're in no hurry to level anyone up, you can sell off the blazes of wisdom too.

3 star and above Servants also give mana prisms, so if you've already hit the max NP level for all of the servants you can get from FP summon, you might as well sell them off whenever you get them. Same goes for CEs.

Sell (burn) 3* Servants and 3*(silver) embers (the exp cards). The Servants give 3 MP each and the embers give 1 MP each.

If you really want to, you could also sell 3* CEs but I don't recommend it since you're better off using the ones you don't want or need to enhance your 4* and 5* CEs. Or to make CE Bombs.

And if you really, REALLY want more, farm the 30AP Ember quest in the daily quest section. You'll get something like 7 or 8 silver embers per run (if I remember right). Then just sell them.

Asides from events and Daily quest rewards, those are the only ways to get Mana Prisms.

If you really want to farm them as fast as possible, just spam the 30ap ember quest and burn all silvers. You’ll get like 1mana prism/4-5ap

Normal way - farm at 30 AP ember gathering then sell all the silver ember you got.

Event - Buy all the silver ember and sell it. Usually event shop will have around 50-100 silver ember. Some event also sell around 1000 mp.

Roulette - only available during Nero Festival, Christmas rerun(usually limited roulette, 7 time reset), and Christmas. These events usually is some of the best place to get large amounts of rare material, gems and mp. Except it's hell you walking to due to limited time to farm for exchange material. Last Christmas I only manage to farm till 35 roulette box before giving up.

30 AP ember quest. The daily bonuses from 10ap and 20ap ember quests are not worth it, and the 10, 20 and 30 AP door quests are not worth it for the same reason. No reason to do any ember/door quests but 30 & 40 AP Ember, and 40 AP door.

IMNSHO Best way is to do all 40 AP dailies and then spam the 30 ap ember daily until the dailies reset.

You should be able to do the 30 ap dailies about 5 times in a day after finishing the 40 ap ones.

Not counting MP from burning items from summoning this should give you about 45 MP a day.

Like everyone said, the 30 AP daily is good.

I’d also look ahead at NeroFest and Christmas this year and figure out which servants you’ll need to raise for the most efficient clear times while remaining CE agnostic. Usually that’s Arash + 2 or 3 others with class advantage. Those lotto events are Unlimited Mana Prism Works.