Welcome back, as one who came back himself a not too long ago;

Like others said before me, finish the Main story quests, and unlock and do the different dungeons along the way.
Gear wise, once you unlock Heavensward, the main story line plus a couple of side quests should cover your basic needs but do unlock Clan Hunts at the Forgotten Knight as soon as you can for easy access to iLevel 200 gear once you reach level 60. This should give you the edge you need to easily start running the basic level 60 Heavensward dungeons quickly.
For leveling, Once you reach above the 50's the exp you need to level up skyrockets, the MSQ isn't enough and spamming side quests while possible, is slow. For that you can run Palace of the Dead, it gives a ton of experience points for every 10 floors you clear and aside from that can give you a nice iLevel 235 upgrade-able to 255 weapon to start with while you work on your Relic, if you even want to bother.