Did I attach the attachment before pressing send?
Before you send out a cold email, read it aloud, and then ask yourself this: Would I want to have a chat over lunch with the person who sent this email?
If the answer is “No”, don’t send the email.
Edit, change and fix as necessary.
Unfortunately this “stop, read, think, edit, send” process is only ever applied by the clue-ful, so stating it is redundant.
Everybody else will just hit send.