Yes! You can practice abbreviating just like anything else.
Think of abbreviations as falling into two broad categories:
(1) A word or concept that will come up repeatedly. For instance, there are all kinds of contrast words: yet, but, however, although, nevertheless, ... They all mean the same thing in the end: BUT. So abbreviate all of those with that short and sweet word: BUT. (I do actually write that down in all-caps in my notes. That's why I'm doing so here.
Another might be any kind of language that indicates cause-and-effect. For those, I don't write down any cause-effect language at all. Instead, I use a horizontal arrow, and I know that whenever I use a horizontal arrow, I'm indicating cause and effect. (That is, I don't use a horizontal arrow for anything else.)
In general, for these kinds of things, come up with how you want to jot down anything that falls into that category. It may not be an abbreviation of the actual word that was used.
(2) A word or concept that is fairly unique to that passage. For instance, they might give me two technical terms that are distinguished from each other in some way. I don't necessarily need to know huge details about those two terms (nor do I need to know their official names), but it's probably going to be important for me to be able to distinguish between the two.
eg, see the passage on page 404 of OG2016 or page 408 of OG2017. I'd abbreviate the two things R and P. I don't need to know the official names; the GMAT isn't going to test me on facts. I just need to know that there were R's and P's and they had a different way of looking at things.
I may also run across words that didn't fall into category 1 but I don't feel comfortable using just a single letter to abbreviate. In that case, I either use the first few letters of the word or I think of a shorter synonym.
For instance, in the first sentence of the passage I just referenced, I might write "odd but true: 17c W --> fem, IDed w/Rs not Ps"
"odd but" is from the passage
"true" is a shorter word for "indisputable"
W = women (a standard abbreviation I always use for women)
--> signals that these women became feminists / were "the forerunners of modern feminism"
Final note: I didn't naturally do all that from day 1. I had to practice it and develop my own shorthand over time. So study this just like you study anything else. When you finish a new passage, one of the things you ask yourself is whether you could do any better with the notes. Was a certain abbreviation confusing to you while answering questions? How should you do it differently next time? Which "category" of abbreviation is this?
Also: Did you write something down that, in hindsight, was too detailed? How will you know that next time, so that you don't take the time to write that all down? Did you not write something down that turned out to be important? How will you know that next time so that you do take the time to jot it down? Etc.
No, you do not need to write the simple story on the test. You're telling yourself that mentally as you gain additional understanding. But, while you're getting better / learning to do this, you may want to write out the simple story. You may decide to go back and re-do some passages that you've already done and actually take like 10 minutes to think through: what should the simple story be and how do I know that? What are the specific language clues that tell me what to focus on and what to set aside as too detailed?
See here for more on RC:
https://www.manhattanprep.com/gmat/blog ... rehension/And on CR:
http://www.beatthegmat.com/mba/2015/12/ ... stion-typehttp://www.manhattanprep.com/gmat/blog/ ... reasoning/Another problem I face is that I the best way to a understand everything in a passage is reading each sentence separately instead of a paragraph.
I agree that this is the best way to understand *everything* in an RC passage.
Your goal is NOT to understand everything in an RC passage. Follow the link above to the RC material to understand why.
p.s. I'm not sure whether you have our books, but there are sections in both the RC and CR books that talk about how to create maps, how to abbreviate, etc. So you may want to review those if you haven't already.