Prioritising AP expenditure

If you have not progress through all the story nodes, I would suggest finish them off whenever you could. Personally one of the annoying thing in this game are some of the events are story locked, so if you don't finish specific story node, you are locked away from event which is not good. because events are the best way to get mat you need for servants.

Otherwise if you done all your story, I just finish off all the x3 & x4 dailies for mana prism, and then start farming whatever you most needed, whether it's qp or certain materials or exp cards.

The 40 AP Exp daily. If you've hit a wall on the main story, then your primary issue is probably needing to level servants, so grind exp.

You'll want to do the main story during "1/2 AP on main quest" weeks. We're in one right now (ends 3/11), and there will be another one in April.

You'll want to complete the main story through Solomon by the end of April, as May will have an event that you can't play (and a welfare servant you'll want to get) if you haven't completed Solomon.

If you've hit a wall story-wise, then leveling Servants seem to be the way to go. As already mentioned above, players can't participate in some quests if they're too behind in the story. (Prison Tower needed London to be cleared, SE.RA.PH. needs Solomon to be cleared, etc...)

Asides from that, it depends. If you're lacking Servants, farm the 40AP Exp in the daily quests to level them up. If you're lacking ascension materials, then you'll most likely have to farm them unless they're in an upcoming event (seriously though, farming materials can be very annoying if RNG isn't on your side).

You could also finish up all the free quests if you haven't yet. If you're lucky, you might gain a few ascension mats while clearing them in addition to the Saint Quartz you get per cleared node.

If you have lots of high level Servants and a lot of extra materials already, then farm QP from the 40AP quest in the daily quests. Leveling up skills gets very, VERY expensive real quick. Even 500,000,000 QP won't last very long if you intend to level their skills past level 6.

The way I do it is I spend the first 120 ap out of the 288 AP we can generate in 24 hours doing all the 40 ap dailies. Then, I do the 30 and 20 AP exp card dailies burning all silver cards I don’t need for servants to get more mana prisms.

From here depending on what Dailies were available and which servant I am working on I use the rest of the 118 ap I can generate either:

1) working on free quests/interludes/rank ups/ etc for saint quarts
2) repeat the 40 AP exp daily to get my characters levels up
3) repeat the 30 AP exp daily to sell silver cards for more mana prisms
4) work on the 30 and lower training ground dailies (if they have mats I need like ghost lanterns) for mats and mana prisms
5) farm the 40 ap QP daily
6) farm ascension/ skill mats from free quests

Number 6) I only do if I am really close to what I need or just give it one or two tries a day and then focus on repeating dailies.

Right now I have a new 5* and a new 4* servant I am leveling up so I mainly repeat the 40 AP exp daily.