The Fangirl's Guide to the Galaxy - Sam Maggs
Short and sweet: covers the main fandoms, internet etiquette, what to do at your first con (I'm hoping to go to Nine Worlds next year, so that section was particularly eye-opening), and feminism in fandom.
My one complaint would be that it's very America-centric (I live in the UK), so some of the resources for finding local geek meetups etc. might be of limited use. This isn't a very fair criticism, though.
I'll definitely be going back to it to check out some of the websites when I actually have some time to spare (i.e. after NaNoWriMo).
