So I noticed that some materials are extremely rare and hard to get outside of getting them from events. I only know of the crystallized ore and the heart of the foreign god so far. Are there any other materials I should focus on clearing out first? (after event ce and servant ascension mats of course)
Materials that have a gold boarder are much rarer drops. They usually come from single large enemies rather than sets of smaller enemies, so there are fewer enemies per quest that have a chance of dropping them coupled with a low chance of being dropped.
Consequently they are also usually the most expensive materials in event shops.
Crystallized Lore only appear during events and via the Rare Prism shop (or they will be in there eventually if they aren't already), thus you usually want to grab that from an event if you are F2P.
Also, if you have any servant that requires Shells of Reminiscence (which I believe Santa Jeanne Alter will), you usually want to grab those from the shop, since outside of event shops (and the Summer Events) they only currently drop from a single mission, and are rare drops at that.
Aside from that, it usually becomes a case of 'What you need' in regards to grabbing, but usually grabbing the Gold Border materials from shops is always a safe bet. All though some 'common' things that might be in shops (i.e. Evil Bones) are also usually things to grab, since a lot of servants use those and use high amounts of them.
Whatever you don't have ;)
Generally I'd say the older materials are more important since they are used by every servant in the game, while newer materials only apply to the servants released after them.
The soon to be released Ishtar is an example of this. If I manage to roll her she'll be my 2nd servant that uses Scarabs and Lamps, but the rest of her materials have heavy competition.
