Keep your executive summary short and to the point. Don't write more than two pages if you can possibly help it, although a major study may require five or six pages. A page to a page and a half is ever better. Work from as outline of the major points to help you keep it short. Colorado State University advises that one way to address the issue is to copy the main points and then edit them down to the bare essence for the executive summary.
Use clear, easy-to-understand English; don't use jargon, but clarify any terms your audience may not understand. Avoid long sentences and don't use big words when small ones will convey the same meaning. The idea of an executive summary is to provide clarity, so stick to simple language.
Use a formal, businesslike tone. Maintain a consistent voice all the way through. Colorado State University suggests that you record yourself reading the executive summary and then listen to how logical your text sounds. Although people will read the executive summary, give it the oral test to make sure it sounds as good as it reads.
Follow the proper structure of an executive summary -- introduction, terms of reference or subject matter, methods of analysis, findings, conclusion and recommendations. Don't backtrack. Write a strong thesis statement that sums up the entire report, and then link the conclusion back to the initial statement to tie the executive report together. In the body of the executive summary, start with the most important points and don't get sidetracked.
Adopt a detached, third-person style and don't use the word "I" under any circumstances. The executive summary is a formal document, so keep it that way and avoid any personal interjections. In terms of format style, the University of Wollongong advises the use of bullet points for recommendations and conclusions.