Go on college visits. Go visit some colleges. Any colleges. I know some families will plan a summer vacation around doing some college visits, and that's great if you have that opportunity. But even if you don't, just get yourself to a few colleges and visit. Take one of their tours for prospective students--even if you don't plan on applying there--or even just walk around by yourself. The point is to get familiar with a few schools so you'll have a better eye for knowing what you're looking at when you tour schools you're really interested in. If you've got an afternoon free, and you probably will, and there's a university near you, and there probably is, then go get familiar.
Think about going to a new type of restaurant, one where you're really unfamiliar with the type of food. Maybe Indian, or Thai, or Israeli, or Ethiopian, or anything. When faced with a menu of things that you've never heard of, you've got to ask a lot of questions or just pick blindly and hope for the best. If college campuses are unfamiliar to you, then you have the same problem when you don't go on many visits. The first one you visit may seem really impressive and become your dream school...just because it has some basic things that most schools have, but you don't realize that. Or maybe the first few are completely overwhelming and you don't realize what questions you have until a week after you've left. You have to ask a lot of questions or just hope for luck. It's better to get these experiences over with before you start doing the tours that really count. Make yourself as familiar with college campuses and tours as you can. That way you'll know when to really be impressed, and you'll know when something is common.
Put together a game plan. You don't need to start on your applications yet, but it helps to have a plan for how you will go about finishing your applications. Here are some questions to ask yourself to get an outline ready for your next semester:
What personal qualities do you want to project in your application? Example of the kind of qualities I'm talking about include resilience, passion, intellectual curiosity, initiative, talent, creativity, empathy, and leadership. Think of one or two of your strongest qualities that will be the focal point of your applications. Your essay will center on these qualities, and you'll try your best to arrange for your recommendation letters to center on them.
What concrete evidence do you have--other than grades and test scores--of those qualities? What stories can you tell that exemplify those qualities?
What are the primary qualities of a college that will be a good place for you? How, other than by looking at someone else's rankings or comments, will you know when a school is right for you? It helps to have idea about this before you start looking too closely at individual schools. Knowing if a school has what you want can prove difficult if you don't know what you want.
Is there a school for which you think you should apply early? Why?
What are the major application deadlines? How do those fit with the rest of your schedule, both at school and outside of school?
What are the gaps in your understanding that you need to fill in? It can be quite difficult to know what it is that you don't know, but make sure you've thought through the application as best as you can and don't find any major holes in your timeline or knowledge.
Talk to your family about money. By the end of the year, you're going to need to send away forms with very detailed and personal financial information, including your parents' tax forms. You're going to decide where the line is between "affordable" and "unaffordable." You're going to to decide how much you and/or your family is willing to borrow for your education. The sooner you begin these difficult conversations, the better. They rarely go well the first time around, so you don't want to wait until the deadline to have the first time around.
Draft some essays. At this point, don't worry about the prompts or the guidelines. Simply ask yourself "what qualities do I want to show colleges, and how can I best write about those qualities?" Start to put together your story that you want to tell. What is there about you that is important and can't be seen on your transcript? This is what you want to show in your essays, so go ahead and get going on those.
Narrow down your list of colleges. There are around four thousand colleges and universities in the US to choose from. By then end of your junior year, you want to have that narrowed down to about 100. By the beginning of your senior year, you want to have that narrowed down again to about 25. By application time, it will be narrowed down to between four and twelve (for most people), and by May 1st, 2020 it will need to be narrowed down to one.
Take care of yourself. The junior year is the most difficult for many high school students. You've just finished yours. You need to prepare for your senior year and college applications, but you don't need to neglect your immediate well-being. Get rest. Read something for pleasure. Have a long talk with an interesting person. Ask some good questions instead of always being the one called on to answer questions. Be a person, and be the healthiest one you can.