Because all the books are set in the same world I'm often questioned about the reading order. As of now they are not serial.
The Staff of Naught and the Hammer of Fire are completely independent of one another with different characters and set in different eras.
The Staff of Sakatha and the Sword of Water involve the same protagonist, Jon Gray, and his friend but they are not direct sequels and can be read independently. The Staff of Sakatha takes place about a year before the Sword of Water but it is not necessary to read one to understand the other and events in the two are largely separate.
The fifth book will be the Spear of the Hunt and it involves different characters and is set in a different era that the other four. It can be read independently.
The Staff of Naught and the Hammer of Fire are completely independent of one another with different characters and set in different eras.
The Staff of Sakatha and the Sword of Water involve the same protagonist, Jon Gray, and his friend but they are not direct sequels and can be read independently. The Staff of Sakatha takes place about a year before the Sword of Water but it is not necessary to read one to understand the other and events in the two are largely separate.
The fifth book will be the Spear of the Hunt and it involves different characters and is set in a different era that the other four. It can be read independently.