SQ

There's really no other way to ge SQ faster unless you buy them.

Asides from completing story and event chapters/sections, you can also do interludes and rank-up quests (though all of them are one time things).

Asides from that, login everyday even if you don't play since you get 4 SQ per week plus 1 summon ticket from the weekly login streak. You get an additional 2 per week by completing the Master missions. You also get a bonus after logging in for a certain number of days (no necessarily consecutively and this does not reset like the weekly one). After the first 100 logins (which give a total of 50SQ if I remember right) , you get 20SQ per 50 logins afterwards.

On top of what JessM mentioned, increasing bonds between 6-9 for 3 star - 5 star servants also gets you SQ, it's a slow process, but it's still something

Buying