This is some general self-editing advice that will save you a ton of money if you're looking to self-publish or even just clean up your MS before you send it to a proofreader. By eliminating all these things in your MS, you also get your reader that much closer to your story, and into your story world, which is what we all want, right?
Words & Punctuation to Seek and Destroy
But Generally any use of the word "but" when it's not a conjunction joining two separate actions in the same sentence (example: "She wanted to go but he stopped her.") is a big no-no. "But, he decided..." Nope. Don't use it as a transition. Just go straight into, "He decided."
Then You may use this one but choose when and where you use it with great care and use it judiciously. Arbitrarily set a number of times you use it -- 3-5 times in the entire MS, let's say. Color-code your text in Word (for instructions on how to do this in Word, click on this blog post, Editing Visually: Colors) , find them all, and decide which 3-5 you are keeping. Then seek and destroy the rest. It can become a crutch to show story progression, which is totally unnecessary. Your story moves forward, naturally. You don't need transitions to tell the reader your characters are moving forward.
So Cut this one every time it appears. This is a seek-and-destroy mission. It bloats your word count unnecessarily.
Well Ditto. I love this one, I do, because I use it so much when I speak, and it's a part of natural dialogue, but like it's sister, "Um," which we NEVER use, it's also gotta go.
... Ellipses. I'm in the process of eliminating these myself. I dearly love them to show pauses, but pausing in dialogue or even worse, action, causes the reader to pause and you don't want that. They're a crutch. Allow yourself a set number in the MS. 5. Color code, evaluate and eliminate the rest.
-- Em-dashes. I love these too, but again, they've gotta go. Know when you employ them as a crutch, and then don't. I tend to use them instead of : (colons) to denote lists, and to set clauses apart when I should be using commas. Why not use them? They give the reader time to pause and think, and you don't want that. You want your reader engaged all the time. It's how they get into your story world, up in their heads, and stay there.
Next, finally Transitions in fiction just aren't necessary. Trust your reader to know the action is moving forward in time. I know, we're trained to add them in academic writing, but forward is the logical progression of a story. You don't need to remind your reader of that. The only time you'll specifically note time passing (via showing a setting change, for instance), is if it's moving backward or sideways (think time travel, or flashbacks, folks). If it is, you have to note it, call attention to it, because that's not the usual progression of events.
Dialogue tags. Know that the current writing trend is moving away from them entirely. If you can, eliminate dialogue tags and use a character action (an action beat) immediately after the quote to show who's speaking. That's what I'm seeing in most of the MG books right now (published 2018 and later).
Speaking of dialogue tags. This is a MS line formatting issue that I see frequently. Format lines of dialogue and action in such a way that the reader doesn't get "breaks" from the action. You want dialogue & action to be seamless. In other words, don't separate lines of dialogue from the character's actions. It's best to combine them.
Your readers will inherently know who's speaking, because the action after the quote is done by the character doing the speaking. Also, you get the added benefit of not having to repeat the character's name in later actions in the same paragraph. If you keep all dialogue & action together, consistently throughout the MS, your reader will trust that's what you're doing throughout the story.
Now, it's OK to deviate from this format to highlight very, very, very important actions or lines of dialogue. But again, be judicious about it. Deviate a maximum of, say, 3-5 times in a MS, during pivotal scenes only (identify your scenes independently and evaluate, folks), for best gut-punch effect on your reader. If you're consistent in how you format the MS, the association between quote (character) & action (beat) becomes automatic in the reader's mind.
Verbs. Check for what I call "doubles," most frequently found as "start / started" and then an -ing form of a verb. Example: "...started walking ..." These can almost always be edited down to one: "walked". Another one to watch out for is "begin / began".
I also generally caution writers to double-check usages of "have / has / had" to make sure they absolutely can't be cut.
"Hads" to Keep
"He had warts." Keep, every single time. It's the possession form of the verb, "to have." If you can substitute the verb, "possessed," keep it.
"Hads" to Cut
However, generally speaking, when using the past participle form, "had walked" for example, it can almost always (I say almost, because sometimes it can't) be shortened to the simple past, "walked." If the action is completed, done, over with, fini, kaput, use simple past. I see writers slip into "had eaten" "had changed" "had visited" when the simple past of these verbs is the stronger, more concise construction, because the action is done. The character's not still doing it. Only use "had" in its participle form if the action is still ongoing. "They had changed the number of archers, from 25 to 50." In this instance, it denotes the number of archers is STILL 50 and perhaps the Captain of the Guard is still in the process of staffing all 50. You'd use it. You'd have to, unless the King changed it again to 75, in which case, go with simple past.
Adverbs. Those pesky -ly words show, don't tell, and some, like immediately, suddenly should be used rarely -- like once, in an entire MS. Save it, until the climax, when it is, genuinely, sudden. To convey the "sudden-ness" of other actions and reactions during your story, you should use other means: verbs (actions), adjectives (description), placement of lines of action independent of dialogue (line formatting), short succinct sentences to create a staccato feel, etc.
Adverbs are wonderful in that they can save on word count and I've seen established, awesome MG and YA writers use them liberally. But they're all on traditionally published, Big 5 books 2 or more. So debut MS -- hunt and destroy. Subsequent MSs, after you've got an agent and a publisher clambering for book 3 and a tight deadline on book 2 -- eh, well, the rules are always relaxed when money's to be made.