Here’s an article in today’s Washington Post along the topic that this thread took: http://www.washingtonpost.com/opinions/no-more-application-inflation/2015/04/17/9d0863ea-e202-11e4-905f-cc896d379a32_story.html?hpid=z3
About some schools not being perceived as STEM schools or whathaveyou: the general public may not see UIUC or Cornell as “engineering” schools, but businesses who hire engineers do. Brown, for example, may be more selective overall, but chances are a future engineer would not find it to be a better choice. Choosing a school just based on its selectivity and brand name to the “general public” is probably not the right way to go, especially if your major actually matters for your future job. What I mean is, some jobs do not require a certain major. You could get the same job if you major in history, poly sci, psych, English, etc. Just graduating from a good university is enough in this case. Some jobs do require a certain major (like engineering jobs). Graduating from from schools known to be good in those circles (even if not known by the “general public”) would be beneficial.
Back to the original question: The only thing you can do is your best when it comes to the SAT and ACT. Once you know how well you have done, then you can start looking at colleges to see what might be a good fit with your stats and interests.