Keep doing everything you were doing before, plus...
Take the PSAT again. This time it is the qualifying test for the National Merit Scholarship Competition.
Take the ACT and/or SAT. Many students find spring semester of junior year to be the ideal time to start taking the ACT and SAT.
Look into SAT subject tests if you are planning to apply to elite schools (Ivies, MIT, Stanford, etc.). SAT subject tests are similar to AP tests, and some elite schools require you to take a couple. They are not offered as regularly as the normal SAT, so you have to plan ahead.
Start thinking about the kind of schools that would be a good fit for you. How do you like to learn? Where would you like to live? What kind of communities do you want to be a part of? There are lots of college search engines available--Naviance and the College Board website both have one, for example.
Speaking of Naviance, get acquainted with it (if you haven't already).
Attend a college fair or two.
Start taking some official college tours if you have the opportunity.
Make contact with an admissions rep if you are really interested in particular schools, make contact with an admissions rep. Some schools keep track of demonstrated interest as part of the admissions process.
Talk as a family about the cost of college.