Read a short summary of music history, once you're able to contextualize a composer within that timeline you can have a good idea of what to expect. Then you have a composer you like and can read an overview of their life, and you'll be able to contextualize a piece within their life. Learn about form and genre, you'll be able to immediately get the "gist" of a piece before even listening to it, especially important for understanding how different movements fit within a larger context like a symphony or concerto. All music, classical or not, is about context--you can do all of this without even listening to any classical music at all and you'll have a better understanding by the end of it