I haven't taken the new test, I had mine like 6ish years ago. Back then, my advie would have been to buy a router or get a simulator (boson used to have a good one) and just run through simulations/scenarios like constantly. Subnetting is pretty easy once you get it down, and they give you a dry erase board when you sit down that you can brain dump a chart on to. Don't spend too much time on stuff like that, spend more time on the practical shit that will not only teach you the fundamentals but prepare you for the simulation on the exam. Which, at least back then, is where most people choked.