I still would like to know the target schools!? I would have different advice depending on the goal.
Lots of good advice on standardized tests, GPA and class rank being the most important factors. As mentioned they are necessary to get into a top school, but not sufficient. So if there is a top school goal, there definitely needs to be more than just academics and you should build out whatever you can there. It needs to be a natural activity that's been present before sophomore year, not a sudden extracurricular whipped up to hope to impress an admission board.
As you probably know, the top schools don't have any merit based scholarships. But they have need based scholarships. If you can't pay for your kid's school, they will subsidize all the way down to a free ride. So, don't let your kid settle ahead of time for a lesser school getting a merit based free ride. Not if they have a shot to go to a top tier school. Of course if you have the dough to pay for a top tier private school, count your blessings and pay up!
Good Luck,
G
PS: With top tier private school I mean in the top 20 of the country. Don't pay for an unknown liberal arts college.