First things first, know that you are not alone! Several others have struggled with Main Point questions in RC and in fact we've addressed that topic a few times on this forum. I'm going to link you to those other threads so that you can benefit from the wisdom of multiple PowerScore LSAT experts!
Passage Main Point: https://forum.powerscore.com/lsat/viewt ... 33&p=18851
Main Point: https://forum.powerscore.com/lsat/viewt ... 487&p=6424
Be sure to check out Dave's second post on this thread for some good, specific RC studying advice: https://forum.powerscore.com/lsat/viewt ... =2&t=15552
Main Point wisdom from our blog: https://blog.powerscore.com/lsat/main-p ... -the-lsat/
My additional two cents: for me, I find that Main Points in RC are closely tied to author's viewpoint and passage structure--which are 2 things you should be tracking as you read anyway! Author's generally write things and give them to people to read because they want people to agree with them or be informed about something. So knowing the author's viewpoint will get you pretty far toward knowing the author's Main Point. But you also have to think about the passage as a whole. There's a reason the author included each paragraph--and generally speaking, those paragraphs are there to support the Main Point!
So let's say I have a passage that goes something like this:
Paragraph 1: Definition of gray marketing
Paragraph 2: Trademark owners' arguments against gray marketing (author agrees with Trademark Owners)
Paragraph 3: Legal views of gray marketing (author likes the idea of regulating gray marketing with the theory of territoriality)
As I've read, I've thought about what the main idea of each paragraph is and I've also kept track of where the author expresses a viewpoint. So looking at the passage as a whole, I would prephrase my main point as something like: "Gray marketing is a harmful practice and should be legally controlled." That involves multiple paragraphs and is closely related to my author's viewpoint: he agrees that gray marketing is bad for trademark owners (Paragraph 2) and he thinks it should be regulated (Paragraph 3).
Main Point in RC is tricky because you have to think about the passage as a whole and sometimes we end up prephrasing a better answer than the one they end up giving us in the answer choice. Always go back to what you think the author wants you to take away from the passage. And definitely check out those links above for some other tips and tricks!
Hope this helps!