Your grades matter, and your transcript will reflect your performance from 9th grade through 12th grade.  Choose challenging, intriguing classes that will stand out on a resume.  Above all else, you need to be sure you work hard and make good grades.

Choose at least one of those activities you began your freshman year, and invest your time and energy there.  You don't want to flutter from activity to activity; you'll want to show that you're committed to a group or a cause.

Start giving thought to colleges.  You will want to make introductions to any school that you might attend, so it's good to start considering what college should look like for you.

You're going to have a lot going on over the next 3 years, so take notes!  What activities are you involved with?  What groups do you belong to?  What are your accomplishments?  Your challenges?  

Say hello to your counselor if you haven't already.  You guidance counselor will likely have a wellspring of information at the ready and will be an excellent resource for you as you consider college options.

Leadership comes in many forms.  As a sophomore, you need to have your eye out for ways to assume a leadership role.

Contact your college (or colleges) to introduce yourself.  At the very least, send an email.  If you can, though, meet with your local admissions officer - it certainly won't hurt, and it may help a great deal.

Take the ACT once at the end of your sophomore year.  This will help to get you acclimated to the test, and you will have had enough math to answer the majority of the problems on the Math test.

For some schools - most public universities and many private universities - your impeccable GPA and other credentials will gain you admission.  Your list of on-paper accomplishments, though, likely won't get you in to America's most selective colleges.  To do that, you'll need to demonstrate "passion" - and you'll want to start soon!