Q. Do you have any tips or resources about writing an executive summary?

Here is what the Purdue Online Writing Lab says about executive summaries:

Abstracts and Executive Summaries // Purdue Writing Lab

This is pretty vague, so I went looking for a writing guide for the sciences. 

In our database eBook Collection (EBSCOhost), we have a book titled

Designing and Conducting Health System Research Projects, Volume II, Data analysis and report writing

In this book's Table of Contents look in Module 32 on Report Writing. Scroll through until you find part 2 and summaries will be listed with an explanation of how to write a summary.

If my assumption of a science based report is wrong, please let me know, and I can find you a writing guide for another type of discipline.