You ask the eternal question.
The first thing to do is complete your manuscript (since it's fiction) and be as sure as you can that it's as good as you can do, in all aspects, including editing and comments from beta readers and/or your critique group.
Research agencies and make a list of those who handle your type of work. Research the agents in each agency to whom you have to submit. Try and find out their likes, dislikes, who they handle, books they have placed, pubishers they have worked with, etc. Ultimately, make a list of those to whom you want to submit.
Write a fabulous query letter. This is your potential ticket to the ball. If it's bad or fair, you lose. If it's terrific, there's a good chance the agent will read some or all of your work.
Write a brief succinct cover letter which you can alter and use if an agent requests same.
Write a terrific synopsis (for the same reasons as the query letter).
Follow the agent's guidelines when submitting.
Submit to about 8 to 10 agents at a time. I suggest that after the first group is sent you wait 2 months before sending out the next group of 8-10. That way you may get the benefit of personalized responses from some of the first group. After sending out the second group of 8-10, continue to send out groups every 3-4 weeks. There's no science to this, so may you choose to do as others might suggest.
Keep accurate records of what sent, when sent, how sent, names, addresses, replies, etc.
Constantly rewrite (if necessary) while waiting for agents to reply and work on your next book.
Good luck and have patience--you'll need it!
Keep records