if you have the time, as you go highlight each sentence or group of sentences and write a quick explanation of the main idea. this will help save you time, because you don't have to reread the entire passage, just the important information.

picking up reading as a hobby is really the best way. read challenging books, like actual genuine literature, not young adult books. reading is beneficial in pretty much every area of life too. focusing your mind on a book for hours at a time helps with your attention span in this age where most people struggle to focus for a minute at a time, and reading is a really important skill to have in college for pretty much any course. additionally, if you use an electronic reader, you can often highlight a word to look it up or see the definition, and if you're curious like me, you can learn a lot about the etymology, roots, and obscure meanings of words, which is really helpful in building vocab connections in your mind.

it kind of depends on the school, but if you submit an application early, as long as it is before the deadline, almost every school will accept an update to your score. now, SOME schools accept new sat scores even after you've already submitted an application and it's past the deadline, but thats goes on a school by school basis and they don't owe it to you to do so. if you're applying via commonapp, it should have the deadlines for all your selected schools, you should get your SAT score ~2 weeks after you finish the test. just look and see which schools you will have the SAT back in time for.

my current score is 1470, my goal is 1520+