There are a lot of options out there in regards to guilds. You will first want to decide on which server you want to play on. Once you know where you will be playing, you can go the forums for that servers organizations. For example if you choose to play on NA-E (Luna), you would go to the Luna Organizations forum to find posts exclusively from the people that also chose that server. From there it's a matter of meeting new people with similar interests and goals and picking the guild that you feel that both benefits you the most, and feels the most comfortable or exciting to you!

Welcome to the community! If you end up on NA-E toss me a line if you ever want to try life as a pirate!

Depends on what you want

In case you haven't gotten that far in reading up on the game, and are asking about guilds based on the guild concepts found in other MMO's then you should be aware that guilds in this game are different.

First of all, there are several organization types, the governments can be considered one (Kingdom/Dutchy/County/Settlement), and then you got Schools, Guilds, and non-profits (sometimes referred to as associations).

The classic MMO guilds would fall under the non-profit type. Guilds in CoE however are more the historically traditional guilds, a group dedicated to a specific trade and profession. Schools are organizations dedicated to learning, teaching, and research.

So if you are actually meaning CoE guilds, then what guild or guilds you should pursue simply depends on what skills you want to pursue in the game. And yes, you can join several guilds, though you are limited to one per skill/profession type, unless you use disguises.