Q:

How to maximise impact from company-wide communications about my work?

I am working on a company-wide communication about a big project (custom software)) I am delivering.
I never did something like this, and I am no communications expert.
I need to reach out to technical and commercial people, having the biggest possible impact.
Format, content, length, language, details... there must be some basic rules.
What guidelines should I follow to maximise the positive impact of a company-wide  communication about my work?

A:

Your communication should answer "Why should I care?" from the perspective of the reader. Sounds like you may need to do two separate communications, so think about the answer to this question from both perspectives (tech and non-tech).
Stick to the essentials. Don't waste time on a bunch of background or explanation that isn't necessary.  You can always fill in the holes later if needed. Don't leave out information that your reader needs to know, but don't include a bunch of superfluous non-essential details.  The longer your piece, the more likely the reader is going to bail out early.
Break it up.  Pay attention to structure. Split up long sentences, make sure paragraphs and sections are in logical order.
Take time to get it right.  Review what you write and make sure it's crystal clear and as short as you can make it.  Come back to it later if that works for you. Take some time to edit.  Take out non-essential words. 
Second Opinion. Ask someone else, perhaps not familiar with the project to read it and give you feedback before you send to the whole organization.  Is it clear? Do they understand why it's important to them? Any unanswered questions that you could address up front?
Summarize. When you're done, write a brief summary and put it at the top.  This is for people that don't have time or just aren't inclined to go deep.  As a recent hire described this to me "BLUF" - Bottom Line Up Front.  Love that!

