Organise context, request and deadline so the reader knows what to do.
Who must act, and what do they already know?
One or two lines of relevant background — no history lesson.
The specific action, stated once, without hedging.
A real date and time. If it is not confirmed, say so.
Why the deadline exists, in one clause.
Read it back: is the action obvious within five seconds?
Filled example: Please review the attached proposal and confirm the service scope by Thursday, 4 PM, so we can send the client a committed date.
Version 1.0. Personal and internal team use. Examples are fictional. Not a certification or outcome guarantee.