If I were you I’d research a bunch of schools, find out more about them and see which ones you really want to go to; not just for the name. Then start studying A LOT for the ssats, it is not about the subject matter, but instead about how well versed you are with the test format. Since you’re in the seventh grade, you have the next year and a half to find out what makes you excited and what you’re good at — if you’re lucky those two things might even overlap 
remember that every grade you get and every award you win is seen by the schools and just use that to motivate yourself to do better
Honestly just figure out what you want and start going towards that goal, it sounds cheesy and cliche but it’s very true.