The following introduction was written by John Renfroe and published here: Learning Classical Chinese is for everyone (no, seriously!). The article contains an introduction to classical Chinese, as well as many recommendations for books to use, including this one.
Note that there are two editions: blue cover for traditional, green cover for simplified.
This is a thin, very portable, and very affordable dictionary of Classical Chinese usage. It’s all in Chinese, but the definitions are often easy enough to read if you’re at the intermediate level in modern Chinese. A super useful feature of this dictionary (and the other Chinese-language ones I’ll mention later) is that it provides examples of characters being used in Classical texts that correspond to the definition given. Often, you’ll find that the exact passage you’re struggling with is cited, which is super helpful because then you’ll know pretty definitively what the character means in that particular context. Highly recommended for all students.