What to do on a dead week

Whichever you want it doesn't really matter. However it is much easier to farm exp than mats.

I find it much easier to farm mat in events and usually focus on exp, skill up gems, and qp between events and new singularities.

And right now with the doubled super /great success rates, exp is the way to go.

For current week, unless you have no servants to level up, farm EXP cards for the super success rate up.

In a regular week, qp or exp cards. The drop rates for mats are pathetic. Better wait for events.

I have other suggestion, this is some un ''Ordinary'' way.
Watch FGO story, try unique set up, then do level up.
Experimenting weird team comps while do the ember gathering, good luck :)

I got a bunch of great servants along with Jalter. But other Emiya, who I kinda need because I don't have other decent assassins, I'm farming for Eternal Gears. I spent all mine from Nerofest on Lancelot and realized I spent my saved ones for Merlin. Honestly though, we're getting back to back Christmas Lottery's so leveling servants shouldn't be that hard then.