Alliances - Joining An Alliance
The game newsletter and the newsletter (620) available in the game contain recruitment messages for the Alliances. It is best to find an Alliance that suits your idea of what your party is about, and then contact the players about joining. If the Alliance accepts you, they will issue a Join Order, which will appear at the top of your turn with instructions of what to do next.
Something to bear in mind if you join an Alliance is that you may experience the feeling of 'being on the outside' for a while. Many Alliance's guard their information and the existing members of the Alliance may take a while to trust you both IC and OOC.
Another common reason you may feel like 'an outsider' for a while after joining is the Alliance may have been through some intense experiences, the sort of things that build comradeship. It is likely that before too long the other Alliance members will accept new/recent recruits in to the inner circle of the Alliance, so it is generally worth being patient because working with an Alliance is one of the best aspects of the game