How to properly make your team

I guess I cant let the ai decide with auto? That's what I been doing but I think im at my limit as far as I can take that

It's recommended to build your team by focusing on either a single element, or a single attack type. This is so that VCs that give something like increased dark damage will benefit everyone in your team.

But in general, you need to have at least 1 healer/support and a physical tank or a magical tank, which are needed in late game content. They don't need to be the same element, but that would be a bonus.