I recently had an aspiring writer contact me and ask about finding a literary agent. I wrote back that the formula is pretty basic: track down a list of agents and submit a sample of your work. If he/she likes it, you will be asked for “the rest.” If they like the whole manuscript they’ll take you on.
There are lots of avenues toward finding an agent. I found my agent via an article in the Minneapolis Tribune. A Twin Cities writer had a big splash with a book, and the agent’s name was mentioned. I tracked him down and sent him a chapter. He liked it, asked for all that I had, and sold the novel within three months to a New York publisher.
Trade writing magazines like Writer, Writer’s Digest, etc. have useful articles on agents, and sometimes lists of current agents, but the internet would be the place nowadays to find agents. Obviously you must be wary, and use your usual spidey senses when doing business on the internet. A key indicator of an agency's legitimacy is the list of authors it represents. As well, an agent should charge you only if he/she sells your work. Commission is usually 15 percent. This sound like a lot of money, but the larger question is: "Fifteen percent of what?" If the agent can sell your work, be happy to give him/her the money.
Big agency versus small agency is a consideration. Small agencies, often just one person, are agile and attentive, but you are more vulnerable if that agent has any kind of personal or professional trouble (which has happened to me). Giant agencies move slowly and are impersonal, so I would look for a small-to-medium sized agency, one with at least 3-4 agents all of whom have worked in publishing prior to becoming an agent.
The previously-mentioned magazines have useful articles on “submissions” to agents. Try to find one of those and model your letter accordingly. On the other hand, so many people probably read those and follow the boilerplate instructions exactly, that you might catch an agent’s attention by an ‘original’ letter—one that suggests that you are a writer but not a cliche'. A good, fresh, short letter, and of course your gripping, can't-put-down sample chapter.
A more creative approach: Say you read a book recently that you really liked. Don’t be afraid to track down the author and ask for his/her agent’s name. If you can “sell” yourself through your email, which means a short, clear and polite query, then the author more often than not will give you the agent’s name–at the same time making clear that they are not recommending you, but only giving you information, which is fair for everybody.
Securing an agent does not happen via presenting your life story, your "connections", your resume' or your sense of humor as displayed in the world's most clever query letter: it's about the sentences in your fiction submission. An agent cannot sell a dead fish (as they say). If your manuscript reads well–is a good story, well told– an agent will see that immediately and be in touch.