If you're school has a pre-vet club, definitely get involved in that! It's a great resource for opportunities and for making fellow pre-vet friends to rant to down the road. As everyone else is saying, get as much experience as you can!! Definitely shoot your shot to as many veterinary clinics as possible (do veterinary assistant jobs if possible as most will train on site). These will definitely get you a good idea as to everything that veterinary medicine entails. That, and try to diversify as much as possible, as everyone else is saying.
In terms of classes, it can definitely be overwhelming to figure it all out, in terms of what schools want, etc. Most of the time a biology major will cover the pre-requisites (at least in my experience). If you're anything like me, try to plan out what courses you need to take over the next few years in a general few-year plan, ie write out what you need semester to semester basis. If you have an in-state, plan most of the courses around the courses they need, but definitely take a peek at some other schools of interest just to get an idea of what they're looking for.