A simple template for self check-in instructions, plus how to turn them into a link guests can reopen anytime instead of a one-time email attachment.
"On the railing to the left of the front door" beats "the lockbox is outside."
Guests read this standing outside with luggage — a scannable numbered list beats a paragraph.
A one-time email gets buried; a link guests can reopen at 11pm doesn't.
Tell them where WiFi info or house rules are once they're inside, so the next question is already answered.