Reddit reviews The Olmecs: America's First Civilization (Ancient Peoples and Places)

Seconding both of wallaby1986's suggestions (anything by Coe on the Maya is bound to be superb). The Coe and Koontz text is actually a decent starting point for understanding any of the myriad cultures of Mesoamerica.

I'd further recommend "The Olmecs" by Richard Diehl. He's a frequent collaborator with Michael Coe and his book can be seen as a companion piece to Coe's "The Maya."