Hi,
It's good that you're starting to think about your applications early. Applying to college is a lot of work and one way you can help yourself is by starting early. Do not procrastinate on this. Starting early, gives you more time to prepare and ensure that you have the strongest possible application.
In my experience, Top schools look at your application holistically as a package so there isn't just a single particular thing that will guarantee admission. For example, it is possible to for a candidate with perfect SATs to fail to get into Harvard. That's not to say SATs/test scores are not important - a high SAT score does, all things being equal, improve you chances. But rather, it is to show you that it alone is not sufficient.
So how do you get in ? You make sure each aspect of your application is as strong as possible. This includes things like your SATs test scores, letters of recommendation, application essay and the like. For SATs, one way to get high scores is to just take many practice exams. This is hard work (the exam is 3hrs+) but most of the question there follow a certain style and after doing it a few times you will naturally get good at answering those questions.
On recommendation letters, my suggestion is to get letters from people who know you really well and can speak candidly and accurately on your current intellect as well as your potential for college-studies. The contents of the letter matter much more than who writes it. For example, you say you lead your high school computer club. I'd imagine that you have had a lot of interactions with the computer instructors at your school in that capacity and so he/she is really familiar with you and your skills at an intimate level. Such a recommender is more likely to write a strong letter since they've seen and know your work first hand.
One strategy that may help you determine if a recommender is a good fit is to ask them: Can you write me a strong recommendation letter ? Most would be up front if that's not the case and politely decline if they cannot write you such a letter. So if you can get strong recommendation letter from someone at Google/NASA, go for it. Otherwise, I'd get one from people who know you well.
The other part of this is your application essay. Do spend time crafting that. Unlike most of the pieces of the application, this is one part where you have total control and you should use this to your advantage. Most top schools give you freedom as to what you can write about, so put some real thought as to what you'd like to focus on. Suggested topics to touch on include, why are you passionate about CS and how did that happen. It's a good idea to have a close-friend or instructor to review your essay. It helps to get a second pair of eyes give you feedback. Make sure though that your voice and personality still shines through in your essay after incorporating any feedback and making adjustments.
I hope some of this is helpful.
Good luck!