Can anyone catch me up on deckbuilding?

I figured there needs to be some "community" posts on here, and why not ask the question.
I have a decent amount of Rubies, and a lot of semi upgraded and legendary stuff. (I came back after a long hiatus)
How do I build a good deck?

I have a few crowns, so I'll give contribution to good advice.

Note: I am a GM currently, been playing from the start. I get a lot about how pieces work, and when they're good. I'm looking for more of an abstracted thing, like high-costed frontline vs. low costed, what the components of an army are: like some big threat, some protection, some secondary threat, etc.