Now is where you try to understand your identity and your story. Who you see yourself as and who you would like to present yourself to the world. There is a tradeoff between exploration and exploitation and now is the time to explore.
Take the most challenging courses possible. There is no point in taking an easy course. Spend your free time exploring what you want to spend your life doing. What do you gravitate toward?
Whatever signals you discovered freshman year, continue to invest in them. The hard part is figuring out how to invest in what you're interested in. What is the best expression of your interest?
By the end of this year, everything you're doing right now is what makes it onto the college applications. There is no reason to take a gap year. A lot of the summer research programs happen the summer after junior year and applications are often due in early Spring.
Complete college applications by early deadlines. Continue similar academic performance. From one perspective, nothing you do from November to May really matters for college unless you do something catastrophic like fail a class or earn a criminal record. From another perspective, you have about half a year to work on yourself.
If you are reasonably certain you want to go into medicine, focus on taking AP Biology as early as possible. If you live near a university, try to be involved in laboratory research. Try to do as many informational interviews with doctors as possible. Explore humanities with the goal of thinking and writing well.
If you think you would like to pursue a PhD in the future, see about getting into research. Right now, computational research is easy to get into.
If you are interested in engineering, take the most rigorous math and science courses possible in each subject. More than that, find a project you want to build. Document your projects.
If you are interested in a business, do not be afraid to make money. Learn transferrable skills of a business. Try to find ethical ways of making money. Save whatever money you make and reinvest it into your company.