The Spectra Books all take place in the same fantasy world. The books/series are all interconnected but not interdependent, so if you see one that particularly interests you, start there.

This page shows charts that compare the different series. Sort chronologically, by publication order, genre, and more.

More information about specific books and series here. You can also try a free sample chapter from each book or series here. 

Here are a few good starting places:

Mira's Griffin is the first chronologically, a sort of origin story, and it's a standalone if you don't want to commit to a long series.

Keita's Wings 1, The Spectra Unearthed, is the first book I wrote. The Keita's Wings series takes you through the six clans/kingdoms one at a time.

The Seventh Clan is the first Spectra Crowns Tale. The main character is a human learning about the Spectra world for the first time, so you learn as he does.