What best can I do during and after college that will help me to prepare for medical school and then a career in medicine?

Two courses I would recommend are a Latin course and a Logic course. Latin because it is the root of so many words. I took a course called "Latin and Greek in American vocabulary." Logic because it teaches you to think, to troubleshoot, and reason things out. If you plan on working hands on with patients, I would encourage you to pick up some customer service skills. Even a fast-food job would help. Or an entry level job at a hospital. Learn how to LISTEN to patients, and treat them with respect. This will go a long ways towards your success as a doctor. Not all doctors have a good bedside manner. I had problems with multiple benign skin growths, and asked a dermatologist if a growth near my eye was also the same as the others. He took a quick look and, totally nonchalantly said, "no, that's cancer." You will be having to ask people personal questions, tell them things they don't want to hear, and guide them through difficult decisions. Many of them will be much older than you, or of a different race/culture. These are all barriers to communication. Please, learn to be a good communicator, which, starts with listening! Thank you.

Medicine is learned differently that other subjects as during your clinical years in medical school and then during residency and other training you are constantly reading about the diseases you are actually taking care of in real people. So one of your patients has heart failure from a failed mitral valve, you are reading about this disease, and then observing and helping care for this real person who is sick and depends on you. This tends to really make a super vivid impression so that if you are serious about understanding your patients, you will remember what you learn forever.