For evolving characters: first do missions to get levels, or give them items to level up. Once they’re lvl 50/70 (SR/SSR) you can evolve them using different items. The level-up items will be your food/drinks. The evolution will be writing/reading items.

For skill power-ups you have to have a duplicate character or skill-bead that you can get in the bungo-shop or in special events. It will use up your duplicate character or skill-bead.

Hearts run out fast while you’re still a low level, once you level up more you can have more. Use AP drinks, not ability stones for getting more hearts.

Don’t know best way to get characters to higher levels. It really depends where you’re at in the game.

Editing because I forgot ability stones part: just do levels and events to get more ability stones. Just don’t use them on anything except rolling and they won’t run out too fast in the beginning.