An executive summary also differs from an abstract. Unlike an executive summary, an abstract is a very brief summary (200 words or less), usually of an academic or scientific research report.
Organize Effectively
Mirror the organization of the entire report. If the executive summary is in the same order as the body of the report, the reader may easily refer between the two. If you are obligated to organize differently, still make clear the correspondence between the executive summary and the main body of the report.
Subheadings Can Speed the Writing Process
We have mentioned before the advantage of writing subheadings that convey complete thoughts, especially given the constraints on executives' time. If you write a heading for every two to four paragraphs in your report, the reader can read only the headings and still understand your message. Just make sure that each subheading expresses a key point. Together, they should tell a story.
If you have used complete-thought subheadings throughout your report, they can often be extracted and linked together to form your executive summary. Naturally, you will have to edit them a little and add transitions, but this strategy can substantially ease your writing task.
An Executive Summary Should Be Relatively Brief
Generally speaking, an executive summary should be less than 10 percent of the length of the entire report and less than 10 pages long. Remember: this is a summary. Yes, the details are important, but your executive summary is not the place for them.
Write the Executive Summary Last
If you write the executive summary last, you will have had a chance to fully articulate your ideas. Some people, unfortunately, daunted by the thought of writing a long report, write the executive summary first. If you write the executive summary first, however, it will often sound superficial and may prevent you from thinking your message through. 
