Use QueryTracker.com to find info on agents, use the forums to workshop your query, and when it’s ready, use QT to keep track of who you query, their response, followups, etc. Extremely useful.
Join AbsoluteWrite.com and put your query through “Query Letter Hell”, a share your work forum where you can get *really* useful feedback, revise, and get more feedback until you have it right. Before posting your own query, read those of others, and the feedback, revisions, etc. Practice critiquing them before you read the feedback to help you learn what works, what doesn’t.
Be careful what you say publicly, on forums, etc. One writer had an offer of representation, no contract yet, and replied to a question about the agent on a forum, and was less than complimentary. Even though she used an anon handle, she mentioned a couple of details. The agent rec’d a google alert, saw the thread, and recognized the writer from the details she had mentioned. Withdrew the offer. Discretion and professionalism are the name of the game, never to be forgotten. Badmouth agents/editors/reviewers and they *will* see or hear about it. Who can blame them for not wanting to work with someone like that?
Read agent blogs, as well as those of editors and experienced authors who blog about writing/publishing. Don’t stop there, though. Follow them on Twitter, LinkedIn, Google+, Facebook, any social media you can. Agents will often Tweet something like “Just wish someone would send me a…” going on to describe exactly what you’ve written. That kind of spur-of-the-moment comment doesn’t often make it to their blogs. You can reply that you have it and ask permission to query. Remind them of the exchange at the beginning of your email or even in the subject line, for ex, add re Twitter exchange mm/dd to the subject line. That prior contact can help you cut to the front of the line.
Don’t send queries to every agent on your list right away. Send to maybe 1/10. If you don’t get requests for partials, you know something is wrong with your query. Revise it and send to another 1/10. Repeat until your’re getting lots of requests. If those partials get rejected, you know there’s a problem with the beginning of your book. Revise, query the next 1/10. Repeat until those partials turn into requests for fulls. If your fulls are rejected, you know there’s a problem with the middle or end of your book. Revise, query the next 1/10. Repeat. I don’t remember the exact percentage of requests you should be getting, 15-20%, I believe.
On Twitter, follow the #pubtip hashtag. Lots of agents will tweet personal preferences, things people do in queries that get an auto R, etc. Make sure you follow each agent’s query guidelines to a T. Get their name right – yeah, use their name, not Dear Agent.
OK, this reply has turned into it’s own book… The biggest thing about querying is *Never* send out less than your absolute best work. Good enough isn’t good enough.