Best advice. Play who you want. And just focus on gathering gems (also don't buy costumes early game. Save your gems for characters and gacha)

But seriously Find a character you enjoy playing and buy them. And if you're wondering you can try characters out in the collection just hit the dumbbell.

Now if your a new new player and don't know which of the first three to pick. I recommend Asagi I didn't start with her (I started with Sakura) but Asagi is well balanced and easy to play and learn her moveset and how to combo it.

But don't worry about Meta. It's dumb since you can just build around it with Supports, and Crest (plus 50% of the cast don't have weaknesses or strength in arena).

But if you want to know I recommend you grab these three charcters first.
Lina (She's new but good)
Rin (She's fast In fights)
Emily (She has a healing ability)

And that's pretty much it. Just focus on getting gems and playing for fun!

Oh and remember to have fun and play with both hands on the keyboard at the same time!