Note: A lot of this plagiarized, get over it, it's not my own work and can be found on BG (Link Below)
Before we get started, here’s a few useful links that you might wish to make a note of as they go into far more depth than this guide will.


Rather than assume you're a new player, let’s assume you know what you were doing at 75. Here's some things that have changed:

General Changes

The level cap is now 99 with 5 new Limit Break quests. This has a dramatic impact on the damage dealt to L75 monsters, a large impact on Evasion rates against L75 content, and smaller impact on the damage taken from L75 monsters. A level 99 Warrior has more evasion than a level 75 Thief did. Just let that one roll around in your head for a little while. This makes old events that were once difficult (like Salvage) very possible lowman. If you remember about how difficult L75 Nyzul Isle monsters were, now all monsters from that era are that easy or easier. Duoing Byakko is no longer a challenge and a wipe to him would be greeted with ridicule.
Additionally, there are new merit point caps and categories. Some of the Merit Weapon Skills represent the best available option for their weapon type.

Merit Changes

The cap on Merit Points that can be spent in some categories has been expanded as of the June 2014 patch, and one of them raises the maximum Merit Points you can hold from 30 to 45.

QoL (Quality of Life Changes)

• There are now 7 different storage locations, all with a maximum capacity of 80. Four of them are available to you when you are in the field, though you can still only use gear and equip items from two of them (Items menu, Control-I, and Wardrobe).
  

• You can access the "Storage" storage location from any Mog House now. You no longer have to return to your home
  

• All auction houses now connect to the same AH. There can be only one. /Highlander.
  

• Crafting delay and guild salesroom delay have both been eliminated.
  

• Maps that were previously only obtainable by completing quests have now been added to each city's Map Vendor. No more getting lost!
  

• The Runic Portal in Whitegate no longer requires a permit. You can pay to use it right at the portal.
  

• No more trips to Nashmau to exchange Imperial currency! You can select how many coins you want directly at the coin NPC.
  

• More common and just more sources of Movement Speed. There are boots that give a +12% enchantment and there are common (if not always cheap) +12~18% options for all jobs. You can use them in conjunction with one another.
  

• New high definition icons are accessed by going to the Config Misc. window. Icon Type should be set to 1 in order to use the new icons.
  

• Base movement speed was increased by 25% in the December 2013 update. Gear now increases speed relative to the new base movement speed.
  

• Home Points now unlock when you examine them. You can teleport to any Home Point crystal you have unlocked. Home Points have been added all over the towns, as well as several dungeons (right outside battlefields), and in Adoulin outdoor areas. There are currently 70+. Teleportation is free in the same city as point of origin, 500 gil to farther points, and 1000 gil to homepoints in dungeons/field areas.
  

• Geomagnetic waypoint teleports have been added from Jeuno, Norg, Rabao, Selbina, and Mhaura to each other and to waypoints in many outdoor and dungeon areas from the core, Zilart, and Promathia areas. You spend kinetic points to use this, obtained from crystals and clusters exchanged to the town waypoints.
  

• NPCs have been added in a magic category called Trust, which fill up to three party slots when you are playing solo, unlockable at level 5. They cost 0 MP to summon, and can be summoned in most areas except zones with time limits. You can have 3 of them out at once, and they fill tanking, healing, and damage dealing roles. At this time, there are 54 NPCs that can be unlocked. They can be out with the Adventuring Fellow and a pet. They can be used in many mission battlefields, and the last limit break battlefield, by summoning them before entering the battlefield. The patches in June and July 2014 made them summonable in parties (including Level Sync), but only the party leader can summon them and they can not be used in Alliance. The AI has also been tweaked, so Mihli uses Afflatus Solace and Ayame will open skillchains based on your last weaponskill.
  

• Widescan can now be used by all jobs/levels. It is not as large as the widescan rng or bst get but it still works for local areas.