Rate my roster

I returned last week after a years long break.

Can you advise me what I should be focusing on?
What arena team I should look at making?
GAC teams?
TB teams?
Anything else I’m missing?

I managed to get myself into a guild that covers Heroic raids. I’m abit reluctant to start over from the beginning again, I know it’ll be a grind to get back into T100 or so but all I’m after really is some advice/guidance?