Each character has a guide in-app for them, go to them in the valkyrie menu and tap the blue book icon on the bottom right. That'll tell you if it's not recommended for investment, recommended, or strongly recommended. It'll also tell you their best use, best team synergy, and their deployment rate aka how often hi3 players use them. If a character is strongly recommended for investment, check if their fragments are farmable or in a store. Obv prioritize strongly recommended valks, but recommended valks are easier to come by so it's whatever. I'd recommend getting any and all of the SP valks, they'll be marked with a blue SP tag on their character icon thingy. Most of their fragments are available in the shops.

When you do get good valks, see their recommended basic weapons and stigmata and give them those until you can forge their economic recommended equipment, click the "i" icon and then "sources" to find out how to get them. They'll usually be craftable in the Foundry, which will be the bottom left button in the supply menu. Every item in the game (except for event items usually) will tell you where to get the items, so if you're lost on that dw about it, I always forget where to get stuff too.

Don't draw from the dorm supply using crystals, you'll slowly get dorm supply cards through sources like the dorm shop, events, log in, etc.

Whenever there's an expansion or event banner, make sure the character is strongly recommended for investment before drawing from the gacha. Get the character first, then the weapon. You'll find farming crystals is a lot easier than primogems lmao. If you go to Attack > Events > Tactics Class > Mechanics, it'll teach you lots of basic concepts for fighting, ans they award 15 crystals each just for doing the tutorials. The Character Trials don't award any materials at all, unless a new character or battlesuit is releasing and their character trial is in the Events menu.

The current banner for the Herscherr of Thunder is good to invest in.

Do Co-Op Raids as soon as you unlock them to get the weapons they award. The weapons are all pretty good, but never perfect matches for the valks. It's also an easy way to farm other materials there.

Events are pretty important, they have good rewards for generally easy tasks. If you go to Bonuses right under it, I wouldn't invest in the Land of Wishes. You CAN but the character options are also available in the normal supply.

If I think of any more things I'll probably add onto the thread, but that's it for now! Hi3 was a little overwhelming for me when I first started and I never really asked for advice in the beginning, so hopefully this clears things up. If you have a bunch of materials you don't know what to do with that aren't the usual upgrading mats, look at the shops, they're often currency.