Structure that gets a reply
Put the request in the first sentence. Recipients decide whether to keep reading within a line, and burying the ask under context loses them.
Follow with the minimum context needed to act, then any deadline, then anything optional. Most email is read on a phone, so the first screen must contain the point.
Ask for one thing. Emails with three requests reliably get one answered.
Subject lines
Describe the action, not the topic. "Approval needed: April invoice by Friday" outperforms "April invoice".
Keep it under about sixty characters so it is not truncated on mobile.
Drafting with assistance sensibly
Give the assistant the facts as bullet points and ask for a draft in a stated tone and length. This is faster than writing prose and then correcting it.
Always rewrite the opening and closing lines yourself. These are where generic phrasing is most visible.
Never let a draft state a commitment, price or date that you have not verified.
Tone
Match the tone of the person you are writing to rather than a house default. A short reply to a short email is appropriate, not curt.
Read anything sensitive aloud before sending. Tone problems are audible before they are visible.