Obtain the guidelines for proposals directly from McGraw Hill's website (mhhe.com). Read the guidelines extensively to make sure you follow the protocol required from McGraw Hill.
Write and submit a proposal using the online "Proposal Form" listed on the McGraw Hill website under the tab, "How to Publish with Us." Make sure your proposal explains the concept in a short, concise manner relaying what stage the manuscript is in: concept, draft or completed. Note in the proposal your experience or credentials that qualify you to publish as an expert if pertinent.
Contact a local sales representative for the company if your concept is not accepted on a national level. McGraw Hill has a directory locator to help prospective authors meet with representatives face-to-face to discuss a book concept or draft.