I try to always keep a notebook by my side whenever I'm reading, and I suggest you should too. Because you never know when you're going to discover a hidden gem of a word or phrase or even an entire sentence that really strikes an inner chord and that you'll want to remember so you can later implement it into your own writing.
But don't make the mistake I did... at least originally.
Years back, I would either literally underline the piece with a pen and/or dogear the page while attempting to fold the tip of that ear so it pointed to the proper place. At the end of the week I would spend an hour or so struggling with keeping the book open in my lap while writing down all of the specific words or phrases or sentences by hand. This eventually left me with a big pile of papers which contained a random collection and no semblance of order whatsoever to reference them without wasting valuable writing time.
Since then I've wised up and now try to keep a notebook on hand so when I come across a particular something that tickles my fancy I pause and write it down. I've also categorized my notebook so later, when I'm writing, I can easily look up the appropriate word or phrase or sentence.
The specific categories are up to the individual writer, of course. Something like "eyes" or "sad facial expressions" or anything else you prefer to make referencing them fast and easy so you only have to pause briefly before continuing writing.
Now, let me get this important point out of the way: do not plagiarize entire passages!
The reason for making and keeping your own notebook of hidden gems is to help elicit better writing from you, not to copy and paste stolen material from other writers while falsely claiming it as your own.
For instance, the sentence (concocted off the top of my head just now): "He leaned closer by impulse, inhaling the intoxicating scent of her lilac perfume while captured by the mesmerizing allure within the dusky smolder of her beautiful eyes."
Writing this entire sentence into your notebook of hidden gems for later reference provides you a bounty of references:
"He leaned forward by impulse..."
"...inhaling the intoxicating scent of her lilac perfume..."
"...captured by the mesmerizing allure..."
"...the dusky smolder of her beautiful eyes."
Any of these examples extracted from that single sentence can be used in a variety of ways depending upon the scene in which you implement them. Perhaps you only like "...the dusky smolder of her beautiful eyes" and so use that bit to describe a character's eyes while disregarding the rest of the sentence.
And that's perfectly fine!
There are plenty of Writers' Phrase Books available for purchase for this very purpose, though I've found creating your own provides you better reference material, especially so for novice writers because you will be taking the bits and pieces of your hidden gems from your own favorite authors whose writing styles and voices you wish to emulate.
Sometimes we have trouble saying something the way we want to but we can't spit it out the way we need to.
So let better writers help do it for you!
Having a notebook of hidden gems helps to remove that word or phrase or sentence from the tip of your fumbling tongue and place it upon the page.
And there's no rule that you must use the exact phrase, either. In fact, don't. Instead, use what you like, and change or disregard what you don't like.
"He leaned closer by impulse, inhaling the intoxicating scent of her lilac perfume while captured by the mesmerizing allure within the dusky smolder of her beautiful eyes."
This sentence depicting two potential lovers locked in stare and possibly about to kiss can easily translate into an uncomfortable opposite situation of:
"She leaned away instinctively, repulsed by the overwhelming odor of his cheap cologne while alarmed by the intensity within the cruel stare of his lecherous eyes."
Now we have a woman attempting to avoid the unwanted advances of an unattractive man who is obviously making her feel uncomfortable and possibly unsafe. That's a big difference between the two, and all from just changing a handful of words.
Never forget: the translations and applications of your hidden gems are entirely up to you.
Maybe you're reading a fantasy novel and come across the sentence "The wizard cast back his hood, revealing a lined and troubled face" which you, who also happens to be writing your own fantasy novel, thinks such a sentence would provide the perfect descriptor for one of your characters, but yours is a female sorceress so you change it to "The sorceress cast back her hood, revealing a lined and troubled visage."
See what else I did there?
Not only did I swap genders and occupational titles (wizard to sorceress), I also replaced 'face' with 'visage' to give it a little bit of personal flare from my own writing voice.
You can also use this technique to help you improve your skills as a writer.
We take the sentence "The air was charged with ancient power" and, applying my Never Use The Word Was 99% rule, we improve it to "Ancient power charged the air."
This is a stronger and more active sentence now that we've removed the word Was ('was' is passive poison to 99% of every sentence it infects, excluding dialogue) and did a little bit of a switch-a-roo to the remaining words, and it could describe the immediate proximity of your sorceress as she whispers a dangerous and powerful spell, perhaps.
I do suggest once you use a hidden gem in your writing that you mark it with an asterisk so you know for future reference that you've used it before as well how many times.
Having your own writing phrase book will do wonders for your writing. Just be patient, because making one isn't a sprint but a marathon. It should take you years to create and your writing career to maintain, not weeks or even months. Remember not to sit and read with the intent of jotting down every other sentence. The magic of this trick is to only jot down a word or phrase or sentence if it pops out at you while you're reading, something that really strikes an inner chord and makes you take admiring pause.
Also keep in mind that context matters. There'll be plenty of times you'll jot something down in the moment because it gripped you by the feels then later, perhaps weeks or even months, when you come across it in your writing phrase book, it doesn't elicit the same emotional response.
That's okay.
Don't get rid of it, instead try to make it something that grips another reader by the feels when they come across it in your book.
Good luck!