With multiple books spread across four different series, new readers often aren't sure where to begin. Each series (Daniel Faust, Harmony Black, the Revanche Cycle and the Wisdom's Grave Trilogy) can be read as stand-alones. 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: