If you’ve never pitched the publisher before and this is your first book, include a copy of your resume. Like any other job, you need to tailor the resume to underscore skills and accomplishments relating to the book and your skill set. For example, if you are pitching a book on using a particular graphics package and have a background or education in design, make sure that this is featured prominently in your resume.
Unlike a typical resume, though, you’re may have to include information that you wouldn’t typically include on a resume. For example, if you’re pitching a book on cooking safe and tasty desserts for diabetics, you’ll want to demonstrate that you have experience in cooking (and probably baking) and in writing. If your resume doesn’t show those skills, you need to include volunteer work or outside activities that demonstrate your skills. As an example, I have a friend who has a brilliant, readable, and fascinating manuscript that is a cookbook/history of cooking going from Roman times up to the early 20th C. It has over 800 recipes, 100% of which have been tested, with comments about the history and context. She hasn’t been able to get a publisher interested because she’s not a TV chef and has no visible standing in the field. There are ways around this, but it’s an obstacle.
Even if you look very hard, it’s possible that you don’t have a lot of resume credits to point to. You may be a dental technician during the day, but you have mad baking skills and you really can write very well. You may be a great dental technician, but you still need to make the case to the publisher that you, yes, you, are the one to manifest this amazing idea. Your writing samples are a great way to back your claim up, so if you don’t have a lot of experience that’s on-target, provide writing samples that make the case for you. (This is all much like garnering the experience for your first job, or your first job in a new field. Tailor your resume, cover letter, and writing samples to demonstrate your skills in writing the book.)