The reminder is a quietly important part of hosting. By the time it goes out, people have already said yes. The reminder's only job is to make sure the yes becomes a person walking through the door. Done well it is nearly invisible. Done badly it is either ignored or actively annoying, and both cost you turnout.
Send it at the right moment
The day before is the sweet spot for most events. Far enough ahead that people can plan their evening around it, close enough that it does not get forgotten again. For a daytime event, the evening before works well, when people are looking at tomorrow. A reminder sent a week out is too early to act on and too late to plan around. Time it to the moment someone would actually be deciding how their day goes.
Lead with the logistics
A reminder is not the place for a fresh pitch. The person already decided to come. What they need is the practical detail they will be looking for as they leave the house: the time, the address, anything about parking or what to bring. Put those first and make them impossible to miss. The job of a reminder is to answer where am I going and when, not to sell the night again.
Keep it short
One or two sentences. A line of warmth, the key facts, done. Long reminders get skimmed, and skimming is exactly when people miss the detail that mattered. The discipline of keeping it short forces you to include only what people need, which is the same thing as making it useful. Respect that they already said yes and do not make them read a paragraph to confirm it.
Let the system handle the routine ones
You do not need to write and send these by hand. On PopIn, guests who gave a contact when they RSVPd get an automatic reminder before the event, through the channel they chose. That covers the standard case so you are not manually messaging a guest list the night before. Your effort goes only into the non routine messages, the genuine updates, not the predictable nudges.
Save the broadcast for real changes
There is a difference between a reminder and an update. A reminder is the expected nudge. An update is the address changed or the start time moved, and it needs to reach everyone with more urgency. Keep these separate. If you blast the whole guest list with chatty messages, the one time you genuinely need them to read a change, it blends into the noise. Use the loud channel sparingly so it still works when it counts.