PVP
Your best bet is to find a friend that will give you the 80 wins you need for conq cap, then attempting to BG so the experience isn't as brutal(If you thought the 20-24 bracket was bad). Once you have the max amount of conq gear pertaining to your cap and current honor gear to fill your other spots, it's basically just a waiting game every week for cap reset so you can hit 550 ilvl. Until then you're going to get buttfucked by anyone with 550ilvl, because that's how this game works @ 90. Once you're fully geared though you're still going to get fucked into the ground by every subpar pve nerd @ 570+ilvl, and it will piss you off greatly. If you're not playing on a server like Tichondrius, it's going to be near impossible to find arena partners, so don't get your hopes up for max level 3s.
PVE
Pick up your legendary quest from Wrathion, google all the requirements for that and plan accordingly. You probably won't get your legendary before the prepatch though, so don't expect to get invited to any serious pve guilds. Anyways, hit up the timeless isle for free epics, Q up for the normal scenario "Arena of Annihilation" to get a quick 450 weapon. Once you're @ around 490ilvl, do your daily H scenario as well as attempt to clear all phases of Throne of Thunder and Siege of Orgrimmar LFR. This will probably be one of your most boring wow experiences, but it's mandatory for subpar gear. Once you hit 520ilvl do some flex SoO until you have gear for normal raids. Once you've done normal attempt to do Hs, etc etc.
My Advice
You're arriving extremely late to the party and your max level experience is going to fucking suck once the freshness of it escapes your mind. Do your best to power through that first phase and it should settle out from there. Your ability to PVE on a serious level are still fairly high this late in the patch, however don't expect to get too far in anything PVP oriented. Competent players are going to be almost impossible to find for 3s, let alone grinding out 550ilvl to even be recognized in the first place. Pace yourself so you don't burn out too quickly, and try to have fun rofl. Your best bet is to just play it casual till the xpac hits. That's when the game is going to get fun.