-If your college has a health career center/advisor, you should talk to them about preparing to go to medical school.
-It doesn't matter what you major in but do well in all of your courses.
-Some of your teachers will have to write a letter of recommendation later so build relationships with them.
-get experience in the medical field by shadowing a doctor and volunteering. You can also work in the medical field, do a summer program or a research program.
-make sure you take the required courses to apply (most schools have the same requirements: Bio I&II, Chem I&II, Organic Chem I&II, Physics I&II all with lab and 1 year of English. Some schools have more requirements such as Calculus or extra biology courses)
-after you finish the required courses, take the MCAT
Your school's health careers department will be able to further help you. Here is a link to the list of all the allopathic schools, you can check each school for their requirements: here . This site is also helpful.
You can find more information for osteopathic schools by clicking on this link.
I'd also suggest buying the aamcas book, or borrowing it from the library. You can see it on aamc.org or buy it cheaper of amazon. The book lists info included by every medical school, including # candidates applying and accepted, typical grades, what the schools look for, location, contact info & websites.
The pre-med world is very intense regarding commitment required to excel at all of the science courses, reading up on what is required to be competitive would be a suggested early step so that you can decide if its for you. There are many similar paths (physican assistant, physical therapist, RN, nurse practioner) that are also great routes.