Advance your cards first

If you have S+ cards with Wind, Fire, Water, or Lightning elements, first check if you have corresponding A and S cards to advance them from 8 to 9 stars. Then, if you pull any other stronger S+ cards, swap them in. Aim for 10 stars only when you feel you have a good lineup. In the early game, it's important to boost your combat power first, which will make stages easier to clear. At least, you won't get stuck as often.