Join a group for the weekly world boss (just use the looking for group tool and join a group, just tag the mob and putz around), drops 665 gear. Hit nagrand now (you should've ideally gone there at 98) and make sure you set your loot to whatever spec you intend to play. As soon as you can queue for heroics, join them and chain them. As soon as you can queue for LFR join it and run through each wing. At that point you may be able to join a Normal pug, but it will be rough with the ilvl unless you got extremely lucky.
If you have time to burn, or if you can keep your game open while you work, queue for Ashran and just join an event group and follow them around. You want to hit your max Conquest Points (10k? somewhere around there) and buy 660 gear with it. This is the best way to get high level gear right now, but it takes like 16 hours of sitting in Ashran to max out on CQ. With the points you can get a 660 weapon and then fill in major gaps in gear with 660 (shoulders, helmet, chest, legs).
Also, make sure you start the legendary ring questline now. It requires running some heroic dungeons then a shitload of LFR. After running the heroic portions the give you a ring that is something like 670 ilvl? 680? can't remember, but it is BIS ring for everyone.