Studying for the PSAT is essentially the same as studying for the SAT. The PSAT is somewhat shorter and easier than the SAT. One difference used to be that the SAT offered an optional essay section while the PSAT didn't, but the SAT's optional essay is no longer being offered since June 2021. You can rename the PSAT 8/9, PSAT 10, PSAT, and SAT as the "SAT 8/9", "SAT 10", "SAT 11", and "SAT 12", respectively, to get a more accurate representation of how these tests differ from each other.
Last year's PSAT National Merit semifinalist cutoff scores can be found here: compassprep.com/national-merit-semifinalist-cutoffs. To calculate your score (from compassprep.com/psat-national-merit-faq), add the reading, writing, and math scores and double them (so reading and verbal is twice as important as math compared to on the SAT).
My tutoring resources folder containing all 20+ publicly available real PSAT tests (email me)