Here's a small list of popular books that can help and introduce you to Ancient India. They are all available in English, by the way.
1- "A History of India, vol. 1: From Origins to 1300" (Romila Thapar)
2- "Ancient India as Described in Classical Literature; Being a Collection of Greek and Latin Texts Relating to India, Extracted from Herodotus and Other" (John Watson McCrindle)
3- "The Philosophy of Ancient India" (Richard von Garbe)
4- "Ancient India: in Historical Outline" (D.N. Jha)
5- "The Ancient Geography Of India" (Alexander Cunningham)
