Hi Maia,
It's relatively difficult to answer your question without talking to you/understanding your thought process, a typical problem I work with students on for these questions is understanding the flow/logic of the paragraph in question, and from there you get a much better feel for "best fit" "logical support" "remove sentence" questions.
Let me know if you'd like a 1 hour or less session where we can focus on those types of questions.
By the way awesome on the PSAT, great you're still shooting high but give yourself some credit too!