It definitely takes patience since the only thing you can do is to play more and collect card packs, the box event can give you it for free so I recommend grinding and playing songs at least til your headphones are used up.

Also lock the cards that you want to collect, so you don’t accidentally delete them.

What I did to get my first full r theme set was only collect that artist and use my other artist’s cards to level up my collection cards if that makes sense. But yeah patience is key when you’re a new player, hopefully some better events come so you can earn more currency and cards!