You should try Wanderers at least once, its an easy dungeon and you can get better equipment than the artifact stuff you probably have on.
You will then start doing an endless grind of Amdapor, it has even better loot and its probably the best source of Mythology tomes which you will need to get some of the best equipments in the game. It gives 40 Myth tomes per instance with a cap of 300 per week, so you might want to do one a day.
You can also grind CM, runs take about 30-45 mins, 100 philosphy tomes each run.
After story, technically the stpry continues. You will unlock hard mode ifrit which leads to hard mode garuda and he infamous hard mode titan. Each of these fights drop elemental hiher leveled weapons (ifrit ilvl 60 ----- Garuda ilvl 70 ---- Titan ilvl 80 .
but wait, theres more. After you beat hm ifrit, your relic weapon quest opens up, which is a loooonngg quest to retrieve and getnyour srrongest weapon in the game for your class. During this quest, you actually have to fight ifrit, garuda and titan along with Hydra and Chimera. Hydra and Chimera are nice 8person battles that help move you along in ths quest.
Why would u want ur relic? Because the multitiered dungeon within a dungeon will be accessible after you get r relic (Coils of Bahamut). Its THEE end game dungeon you want to play if youre looking for hard, very difficult team work. The dungeon can last weeks and different groups branch oit and meet back up to compelte it. This is all before all the extra content is released next monh.
In order to efficiently do anythig after hm ifrit, you want your darklight gear which you need to farm philosphy tombstones (type of currency you obtain from primals, castrums and ampador keep). You get the most from castrums (100 each playhrohh). Its better to do castrum M and not P because itsmshorter so its time to grind because you need a lottt of gear for hm titan.
Anoyhet thig you want is your actual relic gear, which is most wanted for coils of bahamut. Your relic gear cost a currency of tombstones of mythology whcih you also get from hm ifrit and up. You getnthe most from Ampador keep (40 Each time you clear it) but theres a weekly cap of 300 so you will be goig for relic for a few weeks before you seriously want to do coils. Ampador keep also gige you 80 philosophy. So when youre done grindig ampador, go back to grinding Castrum M.
If you want to keep playing for the new content, you can also try leveling a class and crsftmbecause your craftnwill make you money if youre looking for housing in the next update.
So basically its HM Ifrit, Relic Quest start which includes Chimera, Hydra, Hm ifrit, garuda, titan, and actually crafting or getting someone to craft/buy ur weapons base). In between all of this, you wany to grind castum m and ampador keep to get dark light (or dont grind and get someone to craft vanya stuff) to fight hm titan. Aftrr hm titan is done and you get yournrelic weapon, its coils of bahamut time.
NOTE: equipment drops from ampador will helo with hm garuda and speed runs of cm along with one of the primal weapom drops. Also ampador is used to grind for your relic job class armor used to get hwlp exteemely with coils of bahamaut. Since amoador drops currency for darklight and relic youre essentially killing two birds with one stone. Buy oncenyou reach your weekly cap for ur relic currency start doing castrum m again because it gives you the most for your darklight.
Darlight is for aiding with HM Garuda and Ampador keep. Full Darklight or somehig equifalent (crafted Vanya) is for geting thru Hm Titan.