http://wiki.project1999.com/Guilds:G...#Casual_Guilds is a great place to start. "Casual guilds" (and ALS, which gets its own "Environmental Guild" category) will tend to be the most welcoming to new players (as opposed to raid guilds which will generally want level 45+ characters).
From there you can click the forum thread or website links for any guilds you are interested in to learn more about them (and, in some cases, make sure the guild still exists; low-level guilds often don't last as long as raid guilds, and most don't bother to clean up the wiki page when they die).