Prepare your material. Before you even contact any agents, you should have a manuscript completed. Agents will not work with writers who have not proved that they can finish a book. Once you are published and have proved yourself, this requirement may be loosened slightly.
Narrow your search for an agent. Focus on agents and agencies with experience working with business publishers. This experience does not need to be exclusive of other types of experience. Other considerations to make are the size and location of the agency.
Write a query letter and a short description of your book. Send them to the agents on your short list. It is okay to contact multiple agents at this point.
Prepare a follow up package for interested agents that includes a table of contents, a brief overview of each chapter and a summary of the target audience for the book. Also include sample completed chapters (up to three) and a biography that details your qualifications for writing the book.
Respond to an agent's interest to your initial query. This is when your relationship generally becomes exclusive. You should not send any further material to other agents.
Choose an agent based on compatibility. You will be working together a lot. It is important that you can get along and trust each other.