I know editing will seem like an endless game of Delete This—like tasks in this post today, lol—but keep in mind that many edits are also expanding things. When we talk about killing adverbs and excessive adjectives, it's because those are likely going to be replaced with more detail rather than less.
Anyway, here is a brief list of things to avoid, just to get you started.
1. Throat clearing
Throat clearing refers to when a chapter starts and there is a page or two of scene and/or character introduction before the story begins or continues. Let the reader learn about your settings and setting changes as they read rather than you spending time forcing the info onto them. World-building is important, but information dumps are overwhelming.
Don't dawdle. Get on with the show!
2. Head hopping
This is tricky, but it largely boils down to limiting internal dialogue and feelings when writing an omniscient story. Too much jumping and getting into the minds of different characters can get disorienting. And while it can be (and has been) successfully done, you want to limit how often a reader has to reread sections. Head-hopping blurs the rules with its inconsistent points of view, leaving a good chance your audience will continue not knowing what to expect or how to get comfortable with your narrative.
If it doesn't retract from your story, keep it to one or two characters—one character per chapter—and ensure the reader knows who they're following.
3. Redundant words
She stood up from the couch.
He nodded his head in agreement.
They blinked their eyes.
She clapped her hands.
What else would be happening in some of these? She's not going to stand down from the couch, so "up" isn't needed. Nodding is already a sign of agreement, and what else is he going to nod? "He nodded" will suffice. What else are they going to blink? What else is she clapping?
If it can be assumed, it's not necessary. She clapped. Yep, we can figure the rest on our own.
4. Politics and pop culture
Unless your story revolves around current events, it's generally a good idea to steer away from time stamping your book.
"Oh, but a reader can connect to my character better by recognizing the song on the radio or disagreeing with the latest political scandal."
I mean, sure. But you run the risk of your work "expiring" when your current event/song/movie is no longer current. You also chance your reader's subconscious automatically selecting plots, characters, and villains who support their own world view
On that note, keep clear of having your characters sing along to songs. Using lyrics in your book that someone else wrote is a big no-no.