You can choose Teacher Wang Li's Ancient Chinese to lay a good foundation for classical Chinese. Ancient Chinese includes writing, phonology, exegesis, grammar and common sense of ancient culture, which needs to be studied step by step. Recommend reference books such as Notes on Explaining Chinese Characters, Chinese Dictionary, Dictionary of Common Words in Ancient Chinese, and Dictionary of Ancient Chinese. You don't have to buy some, but you can borrow them from the library.

If you like history, you can start with pre-Qin historical essays such as Zuo Zhuan, Guoyu and Warring States Policy. Then you can read Historical Records, Han Shu, Zi Tong Zhi Jian and other longer historical biographical literature.

Reading ancient books needs to pay special attention to the comments of future generations, which can help us better understand the contents of the original.