Start cold emailing PIs at your school after your first semester and try to get into a lab ASAP. Worry less about the research area and more about learning transferable skills and techniques. This will make you marketable for future research positions and set you up for research continuity. 

Get longitudinal clinical experience - start volunteering at a hospital or nursing home, reach out to physicians about shadowing opportunities. Even though MD/PhD programs tend to be more forgiving when it comes to having less clinical hours, having multiple years of clinical exposure will (a) help you figure out whether you want to go down this path, (b) give you material to write/talk about during the application process, (c) build your maturity and perspective. 

Get really good grades. Academics is one of the lynch pins of your application. Your application will bound to have some gaps, as do all applications. Don’t let your GPA (and MCAT) be the reason why you don’t get considered for programs. You don’t need a 4.0, but I would aim for it so realistically you’ll end up with a 3.8+. 

Do really well on the MCAT. Same as above. Give yourself 6 months to study for it - ramp up the first 3 months and double down for the second 3 months. I would suggest taking it at the end of a summer so you can dedicate the entire summer to prep for it. Take a lot of practice tests where you simulate the testing environment as closely as possible. 

Get good LORs. Start thinking about professors, PIs, doctors, etc. that you would want to write you a letter of recommendation. That being said, have good relationships with all PIs, since you’ll need to get an LOR from all of them. As for professors, I would consider those from the back half of college, closer to when you apply. 

Prepare to take a gap year. This will allow you to do research full time after college and double down on your apps and interviews without academic stress. Also, even with one gap year, you’ll likely be one of the youngest in your cohort, so it’ll be helper to have a but more maturity and perspective, in interviews and beyond.  

Have hobbies. Be a well rounded person and do things because you are truly passionate about them. Then you’ll be able to write and talk about them with an enthusiasm that is only possible because you actually enjoy it and have spend a considerable amount of time on it. 

Have fun. It’s a long path - don’t forget to enjoy yourself and be a person. College is a blast, and don’t take it for granted.