PSAT scores help please?!?

I'm a sopre right now and I took the PSAT back in October. I only got 1850 out of the possible 2400 and I think that was in the 91st percentile. How could I improve so that I could qualify for the National Merit Scholarship when I take the PSAT in junior year? Also, for the National Merit Scholarship, if you win it, does that guarantee you admission into whatever college you choose + financial support, or is it just financial support? Thanks.