You should not do anything that is boring or harsh just because you think it might “look good to colleges.” Colleges prefer that you are in interesting person, and there’s nothing interesting about wasting your time and energy just because you’re insecure about someone else’s approval. Don’t jump through any metaphorical hoops (or literal ones, either, I guess) based on vague ideas of what colleges want.

What should rising juniors do this summer to be better prepared for college?

Train. You're like a professional athlete during the off-season. You get a lot more flexibility with your schedule and a lot fewer people watching you as you work, but you've got to spend this time productively. Does this mean to fill up your day with summer school classes and be a student every minute, every day? No. Like pro athletes, find another way to enhance the skills you have.

Think about your notable skills and talents, the things that you may want to emphasize on college applications. Now find interesting ways to improve those skills and talents. How can you best prove and improve your resilience, passion, intellectual curiosity, initiative, talent, creativity, empathy, or leadership? The more unlike another high school class or program the activity is, the better.

So, for example, going to a weeklong camp for debaters is good, but volunteering to do door-to-door canvasing for a local political campaign is better. Reading books ahead of time for your 11th grade English class is good, but starting a book club that focuses on foreign or lesser-known books is better. Taking a class for adults at the local community college is good, but teaching younger kids in a summer program is better. The most important thing is that you focus on yourself and the qualities you want to improve, not focus on a vague sense of "looks good to colleges." In any setting—be it a summer job, summer camp, traveling, or staying close to home—do everything you can with your summer time to be a better person, not have a better résumé. 

Push yourself. If you need to work or want a job, that's great. As far as college is concerned, it really doesn't matter what that job is so long as you work hard at it and are reflective about what you learn from the job. As you go to work, remind yourself to work as hard as you can. And when you're done, ask yourself what you learned from that day's work. Those two things matter so much more to everyone than the job title or name of the company. 

If you don't need to work and don’t want to work, then make other plans. And here's the trick: treat it like a job, in the sense that you decide to do your best and be reflective. Even if you have the easiest summer imaginable--maybe you're going to spend two months as a VIP on a cruise ship sailing around the Caribbean--you can still get a lot out of this. Just begin each day reminding yourself to make the most of the day, and end each day reflecting about what you learned. Whatever is you do, it can be useful for your college applications and useful for your productive and interesting life.

Go someplace new. Choose someplace you've never been that you can visit this summer. Geographically, it doesn't matter how close or far the place is, so long as it's new to you. It can be another country, another state, or another neighborhood. Try to get a sense of how people unlike yourself spend their days, and do it with an open and empathetic mind.

Goal of 20. Another way you can make the most of your summer is to give yourself a goal of 20. Make 20 visits to local museums or parks. Have 20 intentional interactions with older members of your family asking them about their experiences. Read 20 books. Watch 20 of the best movies of all time. Find 20 items to donate to charity. Run 20 miles, spread out over as many days as you need. The number 20 is arbitrary, but an arbitrary number helps make a vague idea an achievable goal. Every time you knock out one of your 20, remind yourself to be deliberate and reflective.

What should rising 9th and 10th graders do this summer to be better prepared for college?

Anything! You can do just about anything, I mean it. In terms of preparing for the next three years of high school, preparing for college, and preparing for productive adulthood, there's no magical activity that you really must do to get ready. Do your thing, no matter what it is (within reason--if your current thing is chaotic or self-destructive then take care of that first).

At this point, what you do isn't nearly as important as how you do it. Whether you're doing amazing, once-in-a-lifetime things like volunteering with veterinarians at a wildlife refuge in Botswana or mundane things like babysitting your little brother, you can make the most of it. Be reflective. Ask yourself "how did today go, and what can I do tomorrow that will be interesting?" Every day. Read something that relates to what you're doing. Even if all you're doing is walking aimlessly around the neighborhood trying to find someone to hang out with, stop at the local library and learn about the history of your neighborhood and go inside shops you've never been in before. Take photos of weird things you notice around the neighborhood. Be engaged with your world and your mind, whatever you're doing in the world. 

Write about your experiences. Writing about what you do on a regular basis serves several goals. For one, any college-bound person has got to be very comfortable with a lot of writing, so practicing on your own with your own assignments helps build up your discipline in a way that's more palatable to you. It will also help you maintain and deepen your self-reflection that's so vital for your off-time. You’re not trying to draft college application essays or make it into a novel. You’re just practicing writing in your own voice about what’s interesting to you.

Make a product. Toward the end of the summer, make some sort of product. Select some journal entries to make into full-on essays. Select and edit some photos to make a narrative photo essay. Make an interactive map of the places you visited. Make a book of advice for someone starting the job that you worked. Again, you can do almost anything. The idea is to curate and edit your experience into something that you can share. That's kind of a definition of education, isn't it?

Meet someone new. Right, of course you're going to meet new people over the summer. But what I'm talking about is to proactively and intentionally introduce yourself to new people that you've chosen to meet. Circumstance, coincidence, serendipity, and providence bring all sorts of people into our lives. That doesn't mean we can't or shouldn't work to bring others into our lives through our own intentions and effort.

Practice some form of meditation and contemplation. There's probably no better gift you can give yourself than to start the habit of meditation and contemplation. There are dozens of different traditions and techniques to fit any religious, cultural, and personal background. Here is a pretty solid introduction to 23 of them. Choose one and try it. It doesn't have to be a religious or spiritual exercise. It can just be good relaxation.