Note: most of these commands can only be used by officers and leaders. /ginfo - Gives basic information about your guild

/g <message> - Sends a chat message to all members of your guild

/o <message> - Sends a chat message to all officers of your guild

/ginvite <player> - Invites another player to join your guild

/gremove <player> - Removes a player from your guild

/gpromote <player> - Promotes a player one rank within your guild

/gdemote <player> - Demotes a player one rank within your guild

/gmotd <message> - Sets the guild's message of the day

/gquit - Removes you from your guild

/groster - Gives an entire guild roster (officers and leaders only)

/gleader <player> - Sets another player as the guild leader (guild leader only)

/gdisband - Disbands your guild (guild leader only) Otherwise the guild rank is just a status symbol. You can check your guild rank by opening up your character name. Your rank is listed under your name.

Guild Tips
Use your guild to help each other through the game. Use a guild to find party members and help each other do quests.
Loan each other money for items.
Pool trade skill components for specific people in the guild. This will allow them to get to a higher skill level much sooner.
Share information for players that are stuck or confused.