If you don't already have the Writer's Market Guide that's a great place to start. It's a real must for every writer with or without an agent. The two best places to find agents are first off,
www.agentquery.com It's a site with the names of lots of agents and you can narrow them down by the catergories they rep. Just be sure to read through the post first to be sure that it doesn't say "DOES NOT except adult fiction" as that catergory tool will bring up any post with the catergory name inside of it even if it has the word NOT in front of it.
Preditors and Editors is a great way to make sure the agent you are querying is reputable. Do your research on the agents you plan to submit before submitting. This will save you a bunch of headaches in the future. THe AAR is also a good place to see if a certain agent holds themselves up to a certain ethics code but just because someone is not on the list doesn't neccesarily count them out - many agents have good reps without being in the AAR. I can't remember the websites for these two places but if you google them it will be easily found. There are many orgs. named AAR but the right link will be the one that says Association of Author's Representatives.
Someone who asks you to pay a reading fee or any type of fee for that matter is not someone you want to sign with. (There are some agencies who charge you for postage and copies but the only time this is ok is if the contract says they take those fees out of your royality checks. Still better and less of a headache to get one who only charges commision.) Reading fees are never ok - huge red flags. Normal agent commision is 15%.
Next you'll need a good cover letter. If you've had something published tell them. If not, keep it to yourself. No agent wants to hear. "I've never been published. I'm new at this but I'm awesome." Let your work speak for itself. If you have an adult or novel manuscript you will probably need to type a proposal. Thomas Nelson's site has a great example of one of those.
ALWAYS ALWAYS ALWAYS query first. I know agents who get aggrivated at someone who doesn't follow their "query first" rule and don't even read the cover letter. They just toss it out.
Most importantly - know that there will be rejections and their will be successes. Finding an agent is a difficult task but it's not impossible. Hang in there and remember that if an agent doesn't see potential in your work it doesn't mean it's not there. It just means you have to find the agent who believes in you as much as you do . . . . And a writer doesn't deserve any less.