How to join every major guild

Here is a walkthrough of joining every single guild in the game!

Thieves Guild

First of all, go to Riften and in the market there will be a man named Brynjolf. He will give you a quest called 'A Chance Arrangement' where you have to steal a ring and plant it on someone. If you fail, the quest still completes but there is no reward. You will then be given a quest from Brynjolf called 'Taking Care of Business' where you have to go to the Ragged Flagon to receive further work. To get to the Ragged Flagon you must go through the ratway, which is part of Main Quest 'A Cornered Rat'. When you are there, speak to Brynjolf for further work.

College of Winterhold

There are three ways you can join the college. Firstly, you can wander to Winterhold and stumble across the college. Secondly, you may have a miscellaneous objective to go there when you have heard about it from a court wizard. Thirdly, you can join the college as part of Main Quest: 'Elder Knowledge'. Go to the college and talk to Faralda and ask her if you can join the college. She will ask you to prove yourself and you will be asked to cast a random apprentice level spell. When you have showed her what you can do, she will tell you to talk to Tolfdir which will continue the quest 'First Lessons'

The Companions

When you first travel to Whiterun and pass Pelagia farm, you will see a group of warriors fighting a giant. They will tell you who they are and if you ask to join they will tell you to talk to their leader, Kodlak Whitemane. This is when their first quest 'Take Up Arms' begins. This is a pretty boring and useless quest but even when you complete it you will still need to prove yourself.

The Dark Brotherhood

The hardest guild to join. You may have heard of a strange boy in Windhelm from an innkeeper, or you can travel to Windhelm and go to the Aretino residence. Break in when nobody is looking and talk to Aventus, which will begin the quest 'Innocence Lost'. He will think you are a dark brotherhood assassin and will ask you to kill Grelod the Kind in Riften. Travel to Honorhall Orphanage and lock Constance Michel in a room, which will prevent you from getting a bounty. When Grelod is dead, go back to Aventus and he will congratulate you. Then 'Innocence Lost' will end. Next sleep in any bed in Skyrim and you will wake up in an abandoned shack with an assassin called Astrid. Muhahahahahaha.....