Understand Your Own Requirements
Simply following someone else's requirements does not guarantee a better report. Most organizational and governmental requirements derive from worthy or logical concerns, but rarely do those concerns include readability.
Set your standards early. Make sure everyone involved with the report understands and agrees with these standards.
You must be the reader's advocate. You must also be accountable for how the report is produced.
Spend time describing the final product and considering the time you (and others) will need to prepare it. If you are faced with a "colossal" major report, sign up for a good course in project management.
At a minimum, answer all the questions below. Be sure to fill in all the blanks. If you do not know what to say right now, just write, "I need to think about this"or words to that effect.