You thought plain English was the goal? It's actually a very low standard - the minimum these days. Start with what you would say to your readers, in the context you imagine they'll read it, and you're almost there.
So what's the next level?
Three suggestions to help you achieve more clarity in less time
Be direct - appropriately direct
Say what you mean and say it early so they know why they are reading your report, email, or letter. Could you put your recommendations up front? They'll read them first anyway.
Be direct in paragraphs too. Give each paragraph a topic sentence, followed by supporting information. We call it 'state and expand'.
Use the active voice
'I have assessed the risks', not 'The risks have been assessed'. Write, 'Graph 1 summarises the results' not 'The results are summarised in Graph 1'.
Add humans (It's active's cousin)
'We need to reply to the allegation', not, 'The allegation must be replied to'. Focus on people and action, not just things. It's the easy way to create interesting, natural sentences. Your readers probably won't notice your writing style, but they will read it - all of it.