What are some resources to prepare for grad school econ?

I learned rudimentary micro/macro/int econ in undergrad for an international studies major. I’ve found interest in environmental science and understand that economics is vitally embedded into policy. It might be overkill but I decided to start from the beginning with value theory, I read on the principles of political economy and taxation by Ricardo, and recently finished Smith’s wealth of nations. I started capital by Marx in January and am 3/4 through volume 1. I’m aware that marginal utility has debunked LVT but am interested in reading Marx + critiques of him anyways. I will read anything and am wondering if there are any recommendations to read for learning classical and contemporary economics to prepare for what I’d experience in a masters/phd program and just to shape how I’d go about policy if I pursue such a career. Thank you!