"Read your work aloud."
No, that's not my foolproof tip. However, that statement, which you've probably heard before, is part of it.
I always wondered why I painstakingly agonized over word choice, and why I wanted it to "sound" just right, when most of my intended readers wouldn't be reading my work out loud. Then one day, in English, my professor tossed the textbook aside and started talking about assonance and dissonance. Another day he told me that my narrative "zipped through" until he got to one sentence he "tripped over." Why? Because my word choices suddenly flopped back and forth between ps and cs and ls. The rest of my narrative, however, was easy to read because I used steady amounts of subtle alliteration, vowel similarity, and consonant rhyme. I like my words focused in the lips and tip of the tongue. I tend to avoid words that use the back of the tongue, unless the sound is at the end of the word and flips easily to the tip of the tongue again.
It sounds super complicated and technical, and not at all conducive to sitting down and pounding out whatever comes to your head. It's not. It takes practice to develop a purposeful word and sound pattern, just like it takes time to practice developing a voice. There's a technical and mechanical side to every art. But it's not as hard as it may sound, pun totally intended.
Our brains read words the same way our mouths would. Tongue twisters are almost as hard to read as say. I don't know about you, but when I read extremely dissonant stuff, my brain stops, trips, staggers, stammers, what have you, and often times, I start reading under my breath in an attempt to clear this sewage clog of wordage.
then look at what you name your characters. You'll probably see some sort of pattern. I know I have pet sounds, especially with character names, and I know this because I made a master list of character names and looked for said patterns. There's a snippet in the photo on the right. The names listed are from different works-in-progress of different genres. You can see even from just these few that I gravitate toward hard constanant sounds and brighter vowels, especially long E and short A sounds.
What's the point of all this? Well, when our brains have to work less at processing the means to the end, the letters to the words to the story, it engages us more in the story and less in the text.
So there you go! It'll take practice and experimentation and a willingness to not story-vomit next time you sit down to pants, but it'll be worth it. My English professor will thank you.