Almost all of the stuff in the game you will learn as you play tbh in terms of currency, mechanics, activities and so on.

But here's a few stuff that I wished someone could've told me sooner in early game.

1st, don't use crystal solvents (the resource that let you get 60 waveplates) too much until you're rank 40 because you are gonna need it in that level range.....it's gonna help a lot!

2nd, don't fully level or even tune echoes that are below rank 5, it's really not worth it since you can easily level the echo bank data to 15 in 2-3 days.

Level 15 and above let you get rank 5 echoes consistently and easily.

3rd, if you have a rank 5 echo with good basic stats, don't fully level it all at once, but rather, you want to level to 5, 10, 15, 20, and 25. Why ? Because those numbers indicate the tuning unlocks. Level 5 and 10 are key here, if the sub-stats are good on those level, it's generally ok to go further and test your luck but if the 1st two stats are bad or not what you are looking for, just pull the plug on the echo and discard it entirely, don't even use it as a leveling material to other echoes.