I stumbled across this old post from Brian McGill: https://dynamicecology.wordpress.com/2012/11/14/clear-writing/
An oldy but a goody. I particularly like when he runs through 6 sentences – this is a really illustrative way of understanding what makes a good clear sentence. A good thing to read before another heavy day of re-writing a text!
Another good resource mentioned in the Dynamic Ecology blog post: https://writingajournalarticle.wordpress.com/sections-relevant-to-all-papers/introduction/