1: Finding the Thieves Guild - The Elder Scrolls IV: Oblivion
Unlike the Mages and Fighters guilds, the Thieves Guild does not have a guild hall. Consequently, locating this elusive group is a task in itself. Your path to the Thieves Guild begins in the Imperial City, so make your way over there. To get the guild's attention, you must spend one night in jail. Getting hauled off to prison is simple, but you'll want to make it a minor offense.
A red cursor icon denotes an illegal action. Ensure that there are witnesses, whether it be a guard or a citizen, and follow through with the proposed action. If a law-abiding citizen witnesses the act, they will most likely fetch one of the city guards, who will then make the arrest. When confronted by a guard, there are three available options: Go to Jail, Resist Arrest, or Pay Bounty. Resist arrest, and the city guard will chase after and kill you. That's not our goal here, so pick 'Go to Jail.'
Read one of the Gray Fox wanted posters around the Imperial City.
Alternatively, there is another way to locate the Thieves Guild that does not involve sullying your record. Befriend one of the beggars in the Imperial City, and they will then divulge the guild's meeting spot. To make this an option, view one of the Gray Fox posters around the city, and 'Gray Fox' will then become a dialogue option when speaking to someone. Raise a beggar's disposition through the persuasion mini-game or bribery, and then ask about Gray Fox. If you choose this approach, go ahead and skip the next paragraph.
Once you've been hauled off to jail, you won't need to wait through your sentence in real time. Look around your cell for a bed, and sleep. When your character awakens, he or she will be out of prison. Remember to re-equip your weapon and armour. Then, fast travel to the Imperial City Waterfront. There, open the wait menu and set it to pass 24 hours. You should soon be pulled out of the wait process by a Dark Elf, who will give you a mysterious note.
Meet Armand and the initiates in the Garden of Dareloth at around 12:00AM.
The note instructs you to visit the Garden of Dareloth in the Waterfront at midnight. Fast travel to the Waterfront, turn around, and head through the open doorway up ahead. Once through the doorway, turn right and head straight until you reach a brick fence next to a house. Jump over the fence and stand in the garden. If isn't midnight, open up the wait menu and pass enough hours until it is. An Argonian, a Redguard, and a Wood Elf will enter the garden at this time. Approach the torch-bearing Redguard and select the Mysterious Note dialogue option.