Ok, so I know that it's not very difficult to join the thieves guild, but if you want some instructions on how it's done look no further.
I made a video of myself joining the guild here: http://www.youtube.com/watch?v=1i5jYyZsb_Y
Or, you can read how to here:
Step 1:
- Travel to the town of Riften, located in the bottom right-hand corner of Skyrim
- Enter Riften and proceed to the town square where you will meet a man named Brynjolf
- Talk to him and he will give you your first quest: A Chance Arrangement
- This quest requires you to steal a shopkeeper's (Madesi) ring
- Once you steal the ring you have to place it in Brand-Shei's pocket while he is distracted by Brynjolf
- After this is done, return to Brynjolf and collect payment for your service
Step 2:
- Now that step 1 is completed make your way to the Ratway located under Riften
- Make your way through the Ratway until you reach the Ragged Flagon
- Here you will once again meet Brynjolf and he will initiate your next quest: Taking Care of Business
- This quest requires you to collect payment from 3 people who are in debt to the guild
- If you inquire Brynjolf further about these debtors you can gain up to 3 optional tasks
- Find each person and collect the money, once you have all the gold return to the ragged flagon and talk to Brynjolf
Step 3:
- Once you have talked to Brynjolf and complete "Taking Care of Business", he will lead you to a secret room
- In this room you will be officially initiated into the Thieves Guild
- As soon as you have joined the Thieves Guild, you will start a new quest: Loud and Clear
- After you have been initiated return to the Ragged Flagon and speak to Tonilia and she will give you a full set of Thieves Guild armor

CONGRATULATIONS! You have joined the thieves guild and now can sell stolen goods and complete thieves guild quests.
If you have any questions or comments feel free to reply below.

Thanks,
Max.imus

So nobody needs help joining the Thieves Guild?

Nope.

Cool