After the Main Storyline there are things that needs to be done.

Leveling gathering for mats needed for Crafts.

Crafting things and leveling crafting.

Making a Fortune selling the Stuff you get from gathering such as Shards and HQ Materials.

Leveling the other classes to level 50 to unlock all class/Job storyline cutscenes and cross-skills.

Darklight set for Endgame by farming CM and TP for their 100 tomes per completion

Getting Your first Relic while becoming poor in the process.

Endgame such as Hard Mode Primal.

So what are you all doing now that you're done with the Main Storyline?