Unfortunately, a comprehensive guide about the 'fastest way to level up' in the game 'Guilds of Greybrook' cannot be provided at this time. Web searches for 'Guilds of Greybrook fastest way to level up', 'Guilds of Greybrook leveling guide', and 'Guilds of Greybrook XP farming' did not yield specific results for a game by this title.
The search results provided information on leveling strategies for various other games that involve 'guilds', including:
Sea of Thieves: Strategies such as diving, merchant cargo missions, vaults, world events, and the Fort of the Damned were mentioned for gaining guild levels. Selling items like fish, loot, and cooked animal meat (especially to the Hunter's Call or a Sovereign) also contributes to guild reputation. Completing world events and being mindful of gems to sell at the Hunter's Call were highlighted as effective methods.
The Elder Scrolls Online (ESO): Leveling different NPC guilds (Fighters Guild, Mages Guild, Undaunted, Psijic Order, Thieves Guild, Dark Brotherhood) involves specific activities. For the Fighters Guild, defeating vampires, werewolves, undead, and Daedra, particularly in Dolmens or group dungeons like Alik'r Desert Dolmens, Banished Cells, Crypt of Hearts, and Vaults of Madness, is effective. Mages Guild levels by collecting lore books and completing daily quests. The Undaunted guild progresses by completing group dungeon quests, pledges, delve dailies, and trial quests. The Thieves Guild is best leveled by stealing items and selling them to a fence, or by completing daily quests and heists. Power leveling in ESO often involves grinding in specific locations like Alik'r Desert Dolmens or Skyreach, using XP buffs, and completing daily dungeons/battlegrounds.
Hypixel (Minecraft Server): Guild experience can be gained by playing games like Paintball with guild mates or winning Skywars. Guild challenges, found at the quest master, also award significant guild XP upon completion.
EverQuest II: Crafting writs (rush order or regular) and selling relics to a status merchant are noted ways to gain guild status and levels.
Guild Wars: Power leveling involves killing a high amount of high-level PvE foes, often with the help of a higher-level player, allies, or special builds. Strategies include reducing team size, using experience scrolls, and repeating specific quests or farming foes in certain areas.
Since no information directly pertaining to 'Guilds of Greybrook' was found, specific tips, strategies, or builds for leveling up in that particular game cannot be provided based on the available web search results.