Game Progression
Levels 90-100
No Unlocks This Time
There is nothing to unlock specific to this level range. Just keep pushing and grind out as much zeny as possible. You're most likely low on Adventure Handbook stats so be sure to invest some of your funds into raising your base Atk (or MAtk if you're a mage) so that you do more damage if you've already made your synth weapon and taken it to +10.
Extra Skill Points
By now you'll hopefully have hit job level 40. After this point, you can start allocating some extra points into certain skills. For example, Vulture Eye for archer only goes to level 10 but now can be raised to level 20. These extra points add a significant damage boost the further away you are from a mob.
Every class has several skills that now allow some additional points and these points typically add an additional stat or effect so be sure to review your skills to see if you can upgrade any of them further.
No quest needs to be done for this it just becomes an option for some skills once you reach this point.
Examples of skills that allow extra points to be allocated. They have a yellow + sign and their maximum is higher.
Continue Following the Main Questline
Continue with the main story quest.
Daily Routine
Weekly Tasks up to this point (reset is on Monday at 7am EST):
Echoing Corridor (HARD, don't stress if you can't get this done)
Buy out the Rune Shop in Prontera if you can afford it
Runes are extremely powerful for several jobs and small runes will payoff in the long run since they can be upgraded
Daily Tasks
Listen to the Jukebox for up to 30 minutes
Visit your Guild and purchase some Contributions and Gold Medals with extra materials
For now, try to only use excess materials but don't go nuts. You will get lots of various materials from Endless Tower.
Complete as many dailies as possible
Finish 3 Board Quests
Run up to three of the new level 80 Rift Challenge to upgrade your armors if you haven't already
Work on Adventure Rank in your spare time
Work on upgrading an appropriate weapon, read up on Upgrading Equipment for the finer details
Read up on General Farming Tips to better understand buffs, elemental weaknesses, and more
Targets for Daily Combat Time
Desert Wolf (lv 53)
Metaller (lv 55)
Payon Cave (lv 61-69)
Minorous (lv 64)
Orcs (lv 70+)
Kobolds (lv 72-74)
Petites (lv 76-79)
Glast Heim (81-90)
Glast Heim Hall or Chivalry (90-99)
Tough targets for this point in the game, advised to skip but feel free to farm these if you want their card or materials
Clock Tower F1 (98-103)
Many formless mobs here and mobs are very spread out, hard to target a specific monster here. May want to hold off until you can do Clock Tower B1...
Clock Tower B1 (105-109)