As a War work on all weapons. Level them atleast high enough to hit level 95+ mobs. The leveling is done in alliances due to the FoV pages. They should have been put in about when you quit, maybe a bit before maybe a little after. So show up ask if any openings and ask what page to get experience. The mobs give **** exp per kill but the real exp comes from completing a page.
Game will be very different for you. Was for me and I quit 5~ yrs ago. Run to Jueno, get to port and talk to Joachim. Get Traverser Stone and they start to build. With the new expansion we will all see how that impacts Abyssea, although I doubt it will be different for a while. Mobs in new expansion areas are Tough to 99s.
Find a LS, if you don't have one now, and they can explain finer points. Welcome back to your addiction.