One of the questions I get most frequently is how a person acquires my job - i.e. how do they enter entry-level publishing. (The other question is why do bad books get published, and nobody can answer that to everyone's satisfaction, so I've stopped trying)
The answer is: Craig's list NYC. Job search: Writing/Editing.
No, seriously, that's where all the listings are, aside from the NY Times, and this day and age, by the time the ad goes out, the position might be filled. Check on Saturdays and Sundays, too. My first job was posted on a Saturday night, and I answered within an hour, and got a call on Monday morning. She said she had 100 applicants within a day for a job that paid $10 an hour.
Serious work - full-time work at a publishing house as an editorial assistant, with health and dental benefits - usually requires either an "in" (your uncle works there) or a year's experience. Many people get started as unpaid interns at publishing houses and literary agencies. Some houses even have programs in the summer that offer college credit. The programs work both ways - the company gets free workers and the workers get work experience and a reference or two.
That said, it is not actually necessary to be an intern before you become a paid worker. I came into the industry with no experience working in it and no references. I just killed in the interview. Here are some tips:
(1) Know what a query letter is and how to tell between a good one and a bad one. Subscribe to Publisher's Lunch (in case that comes up in conversation). Read the bad queries people are posting on Writers.net and people's comments on them. Read agent blogs. The key moment of my first interview, where my boss obviously decided then and there not to bother with the rest of the pile of people, was when she showed me query letters and had me analyze them on the spot, and I was able to say things like, "He's comparing himself to Dan Brown - bad. He's listing being a member of the Romance Writer Association [or whatever it's called] as a credit, but anyone can be a member of that. That's not a real credit. And nothing strikes me as interesting in the hook." Etc etc.
(2) If asked what you read, list as many things as you can. Don't be afraid to list your guilty pleasures (mine was "Entertainment Weekly"). Have a good joke ready about why your favorite book is your favorite book. Try not to sound like an English major when talking about literature.
(3) If you're a writer and you're going into publishing, don't deny it, but have an explanation as to why you're not going into publishing just to get "in's" for your writing career. I legitimately went into publishing because I love reading and I love helping writers succeed. My own writing career is separate. It does, however, mean I've been in writer's communities and workshops and I'm familiar with what they're doing. That's not a bad thing.
(4) If you're applying to an agency, familiarize yourself with the client list of the agency if it's available. Read the summaries and reviews of the books on Amazon.com so you can at least said, "I've read reviews."
(5) Smile! Unless you have exceptionally bad teeth.