With multiple books spread across three different series, new readers often aren't sure where to begin. All three series (Daniel Faust, Harmony Black and the Revanche Cycle) can be read completely alone. That said, all of Schaefer's stories take place in a shared universe, where characters and concepts cross over from book to book. If you read everything, you'll catch things you might have otherwise missed, and glimpse the bigger tapestry behind the scenes.
To that end, here's a guide to Schaefer's books from start to finish. So you can pick a single series and read it in order, or see it all: