I admire the people who were able to get into Stanford. It is my dream school. Really wanted to find out the merits the admission officers are looking for. I would like to start a thread to listen to your stories. What made you get into Stanford? High GPA/SAT/ACT? extra-curriculum activities? Summer camps? Would you mind to share the details? Thanks in advance!
Even if you excel in all of the above, you might not get in. Many applicants perform well in all these criterias and Stanford’s acceptance rate is around 5%.
Everything.
Stanford takes a holistic approach to admissions, meaning they consider everything. The most important thing is to take the hardest classes/most rigorous courseload and obviously succeed in it. Do what you enjoy and stick to it. Clearly, getting good grades and test scores are important but no one thing will be the deciding factor (unless you’re a recruited athlete etc). As @UCBUSCalum said, you still might not get in. But picking one thing and excelling in it (like, REALLY excel, (inter)national level will definitely help. Show your passion in your essays.
(I know a lot of this advice is repetitive and seems vague at the moment, but after you finish you will realize the truth in it.)
My kid (non-STEM interest) probably got in because he came across as a real nice, caring kid who had pretty good gpa and scores (not fantastic). Many kids in his high school with fantastic stats did not get in. Go figure. My kid did have though very good ECs (beyond normal in-school high school activities as newspaper, Key Club etc.) in his area of interest.
My theory is that the admission officer got sick of reviewing all the kids with fantastic stats and decided to admit one kid for whom the admission officer felt sympathy or a genuine liking as a person. They probably thought “I really like this kid. Even though his stats are not fantastic, he does show some promise. Besides, we don’t have to offer financial aid to him.” 
If I could take a guess, none of his teachers recommendations ever said “He is one of best students I have ever had etc.” Instead, the letter probably read “He is a good student, participates with a smile and is courteous, doesn’t cuss and is responsible and respectful towards his fellow students and teachers. For example, he opens doors for other kids, brings coffee to his teachers and asks them if they had a nice day, etc.”