1. GPA DOESN'T MATTER FOR ANYTHING!!! Every school calculates it differently. 7.0 at one school might be the same as 4.0 at another. Only class rank matters and what school you went to.
2. SAT MATH is very important. They want 800 or close to it.
3. For extracurriculars, they want you to show that you didn't just participate, but that you competed/won against a lot of others. UIL Math/Science/Number Sense success goes a long way. 5s on all the math and science AP tests is good. All state or area band/orchestra in 6A is really good. 6A district championship in basketball/baseball/track where you beat hundreds of kids in a district can be more prestigious than a 1A state championship where you only beat 100 other competitors. National Spelling Bee, Geography Bee, Science fair is great.
I Can't comment on research because I didn't have any connections, and got in w/o it and without national merit.