You have to research and know your subject.
Find your favorite book.
Look inside the front cover or on the spine of the book for the publishing house.
Most publishers are online now so you should have no problem Googling them.
You should be able to find a list of agents on the website. Read through them.
(If you already know an agents name, find them online).
Ask these questions about the agent:
What are the submission guidelines? (follow them exactly!)
What are the recent sales?
Who is on their client list?
Do I want a new agent?
If you send out your work simultaneously to different agents and get a response from one, send a note to the others letting them know; it will peak their interest.
If you haven’t heard from an agent in 2 months, it’s acceptable to check with the agent to see if they received your work and if it’s been looked at.
Any tips you have on finding an agent?