* Use a few bullet points to put attention on the main points you want to convey.
* Without going overboard, use a tasteful amount of graphic design (bolding one key sentence or whatever).
* Break up a giant nuanced email into sections.
* If something is critical, make it visual: a picture, explainer video, or an infographic can be really useful for something key.
This is harder than it looks. A quote attributed to Mark Twain is "I didn't have time to write a short letter, so I wrote a long one instead." It's a lot easier to go overboard than to distill what needs to be conveyed into the core elements.
Hell, I've learned not to ask more than one question in an email. The first one is the only one to get answered.
If I receive an email and it’s something I can quickly answer on my phone while waiting for the bus etc., I’ll do so and you’ll get a quick answer. If the email requires me to sit down and compose a long response (or worse, read a paper, or find and run some code) the email gets put on a priority queue to deal with during dedicated email-answering time.
If I receive an email with multiple questions, and one of them I can answer quickly, I might fire off a partial answer (under the theory that a partial answer now is preferable to a complete answer much later).