Great question, @Anonymous

Just like you, we here on the QB Community Team have wondered about wording and timing for invoices when you've got a client (or clients) from whom you need to collect. We created the following series of articles to help out with just that:

Frustrated by Late Payments? Some Tips for Tracking Down Your Dollars

Make Every Invoice Work Faster and Better Than Ever Before

The Mighty Invoice: How to Put This Powerful Tool to Work

There are links to more resources from within these pieces as well. I hope there are some ideas in there that help you out!