Hire an editor with experience in editing technical books. Even the best writers have difficulty editing themselves. The editor should have an understanding of your topic and be able to spot not only grammatical errors but also factual errors.
Prepare a press release and an informational packet to send to publishers. Include your credentials and experience and how they make your book the best book on the topic. Collect recommendations from your colleagues.
Create buzz for your book by making radio appearances, local television programs and by conducting lectures that are focused on the subject of your book. Develop a website that you can direct potential publishers to. Make sure it's professional-looking and has all the information a buyer would need.
Approach technical and university presses. Call and find out the editor's name. Send an information packet with a cover letter that briefly explains why your book is different. Follow up with a phone call and listen to the reasons the publisher won't accept the book if they turn it down. Act on that knowledge.
Self-publish your book if you can't find a publisher through traditional means. Arrange for a printer to do a small press run of your book or have a copy shop print copies of the manuscript and bind them. Send copies to technical publications and publishers for review. Follow up with a phone call.
Publish on-demand. This eliminates the expense of a print run. Books can be created as they're ordered or can be made available for download. Downloaded books are more economical and eco-friendly because no paper is involved, and there are no shipping charges. According to Kelly Gallagher or Bowker Publishing, on-demand is the fastest growing segment of the publishing business.