Two kinds of writing
If you're writing for strangers, make it shorter.
Use images and tone and design and interface to make your point. Teach people gradually.
If you're writing for colleagues, make it more robust.
Be specific. Be clear. Be intellectually rigorous and leave no wiggle room.
Takeaway: the stuff you're putting online or in your blog or in your brochures or in your business letters is too long. Too much inside baseball. Too many unasked questions getting answered too soon.
Takeaway: the stuff you're sending out in your email and your memos is too vague.
Figure out which category before you put finger to keyboard!