kkumabunny

I always do really bad because I doubt myself and it takes me a while to understand the passage. D:
Also, my vocabulary is really bad, so that lowers my critical reading score...

chewydog

You know your issues, which is good. Consequently, stop doubting yourself (do celebratory dances when you get something right to boost morale if necessary), read more literature and higher level articles, and study vocabulary in your spare time. You also should check out the guides highlighted in the sticky thread.

teteatete

Devise a method and stick with it. Also, never give up on a passage.

Whether you read the entire passage first, or jump directly to the questions is largely irrelevant, as long as you practice in that way. CR is tough, but like I said, it's a matter of meticulous practice in a single way, as well as a bit of reading brawn.

Method 1:
Read the entire passage first, and fully understand it.
Answer specific questions by rereading the line reference questions, rereading those parts.
Answer any remaining questions.
This way is a bit more challenging time wise, and is more appropriate for faster more adept readers, but it provides you with a more thorough understanding of the passage. Reliable for yielding 700+.

Method 2:
Mark up the text with line referenced.
Read through the line reference and answer questions.
Answer questions as you get to them.
This way is generally easier, but allows for some lapses in understanding, and sometimes you don't catch the full idea of the passage. Reliable for yielding 650+.