Like other posters have said, don’t buy boost points unless you’re getting the 100 per day from the boost sub.
If you are using boost sub, make sure you only activate it when you’re art 100 stage 1 boost. Then you’ll want to prioritize content that costs only 4 boost points (no story or tracking missions) and gives you the most good per stage cleared. So that will be:
Daily Mission > Event Mission (like the recent Halloween event stage 5x per day) > Deluxe Pack missions (beginning of chaos and Mutual enemy) > Memory Mission > Dark Dimension > Special Mission
I just do them in that order until I run out. IF there are no events, that’s enough to do everything listed plus 13 special missions all under boost stage 2 effect.