First of all, make sure you're really ready to read your work in front of friends, family, and strangers, and be sure you've got something to offer that will encourage various venues to host you as a reader. I think it goes without saying, but the more of an "in" you have with the owner, staff, reading organizer, &c, the less well-published or well-known you really need to be.
If, on the other hand, you want to read at Fancy New York City Lounge and you don't know any of the staff there, you'll need an impressive publishing credit or two (or a well-connected friend) to help get your foot in the door.
Next, I'd make a list of the following three types of venues:
1. Places that host readers/reading series where you have a connection with the owner(s) or staff;
2. Places that don't necessarily host readers/reading series but where you have a connection with the owner(s) or staff;
3. Places that host readers/reading series that you admire (but you have no connection with the staff).
In that order! As I've said before: after a certain point, who you know becomes much more important than what you know.
Don't limit yourself to bookstores, either (though they're a great option); cafés, bars, and community centers (your local YMCA, synagogue, community college, library, school auditorium, you name it) are also excellent options.
Once you have your list of potential venues, get in touch with them about a possible reading. A few tips on this:
· If you know the person who runs the readings/venue, give them a call! No-brainer.
· If the venue has a dedicated person who arranges these kinds of events and you're not already best bros with them, call or send a Very Professional E-mail to that person. Call during business hours; shoot an e-mail if it's very early or very late.
· If there's no dedicated contact person, call or e-mail the venue's general number/e-mail address. If you call, be prepared to be handed off to a couple of different people, especially if the place you're calling doesn't usually do readings. Don't lose heart! Or your patience.
· Be professional! If you call, be prepared to talk a little bit about yourself (assuming they ask). If you e-mail, feel free to include a short bio or a link to your website. Remember: the less well you know the venue and its staff, the more established you'll need to be to get a positive response.
· I wouldn't include any kind of sample material with the initial e-mail; most places that are interested in hosting you will ask for it, either as an electronic file (poems, short stories) or in the form of your most recent book.
And that's pretty much it! Once you've cast your net, all you need to do is wait for a response. If you don't receive one, I think it's fair to follow up in a week or two to check in.
If they say no: try again elsewhere.
If they say yes: congratulations! You're doing a reading! Here are some tips for that, courtesy of Brad Phillips.