Two short easy places to start. Of course after that, there are lots. Schroedinger's lecture notes on Statistical Thermodynamics are a clearly thought out gem of pedagogy, it was really his forte. And you don't need to finish the book either.

Khinchin's monograph on Mathematical Foundations of Statistical Mechanics is also incredibly insightful, although you can skip the proofs, and again, the first half of the book suffices.

This will give you a clear, logical, and physical foundation to then go on and read anything else.