Don't Treat Your Game Like A Story Book

When talking abut RPGs I quite frequently talk using narrative terms and lessons used in storycrafting. The PCs should be the main characters. The game should revolve around said main characters. Etc. Etc. However, while you are telling stories in RPGs, it's not a book. Nor is it a movie, comic, or other story telling medium. As such, you need to be careful not to treat it like a book, because the dice - and the players - frequently won't let it happen that way.

No Monologuing
I don't know about your group, but my players are allergic to monologues. It makes them break out in violent action. It's a common thing I've found at numerous tables. Get a person to start monologuing, and the PCs will do something to interrupt it - often starting the boss encounter early. This is just something you need to be aware of as a GM. If it is vitally important to your campaign/story that the villain get to say a peace, you need to make it so they can't be interrupted. There are few ways to do that without losing agency, so in general I recommend not hinging your game on a villain's monologue.

On the other hand, you can use this aversion to monologues for comic effect in niche situations. In a Teen Hero game I ran once, I had a villain named The Steam Punk (he was like 16, cut him some slack) who attacked his highschool junior semi-formal where the PCs were. As a true brainy villain while he had people cowering with his mechanized minions he started monologuing. I did it deliberately as a character piece, and because I knew a player would interrupt him. Sure enough they did. The strong one threw a chair at his head. Everyone had a laugh. Comedy was enjoyed. The fight was on.

Now, not expecting this can cause problems. In another game where I was a player the GM had the boss going into a speech about what he would do. In the middle of the speech I told the GM "I shoot him in the face." The GM blinked, looked at me. I repeated myself. We did a roll, I won. My character drew their gun, shot the guy in the face, and killed him in one shot. Why did it work? Because at the end of the monologue the man's defenses would activate and the fight would be on. By interrupting I got him without those defenses, and what should have been a very deadly encounter was basically a nothing affair.

No 70s Soap Opera Moments
Man, Soap Operas get a bad rap and depending on where you are the group that is the worst changes. Part of the rap for Soap Operas is that the craziest things happen in an interest to keep things, well, interesting. Not only is your mom abducted, but there is a clone and the clone is actually a russian spy that is going to try to kill you.

In game terms this comes across as every NPC the PCs meet is either an enemy, a secret enemy, or a friend who will become an enemy later on. Alternatively, they're a quest giver, or a terminal that exchanges coins for goods and services. In other words, the only characters the PCs meet that get fleshed out and are allowed to be people are ones that are meant to be villains or henchmen and lieutenants of villains.

The next thing you know, the PCs are basically suspicious of everyone that gets screen time outside of them going to them because it's only a matter of time before betrayal. It sucks, and it kills a lot of tension in your game. Luckily, it's easy to defeat. Just have NPCs that recur that aren't villains and never will be. Sometimes the cute boy that likes the ranger is just a guy with a thing for people wearing leather armor and wielding bows. The woman the PCs saved on the road? She's just a friend who will give a place to sleep and makes wonderful bread.

By having NPCs that are just people - be they friends, lovers, shop keepers, or neutral - you teach your Players that not everyone is out to get them. Some people are just people. Which also means that those who will betray them get a fair chance at it.

Other Things Should Be Happening
The PCs should be the main show for the game, but other things should be happening as well. Other adventurers should be running around the world. Other going ons should be, well, going on. Give the world a sense of life. Have things happen. Make them happen around the PCs and not just to them. Let the barman have more stories than a recap of the PCs last adventure. Let the PCs meet other people like them.

You'll be amazed what doors it can open up later on when you have these things in motion. Including opening up different options like a sibling hiring the PCs to look for their lost adventurer brother/sister, or the PCs getting a note from another adventurer they know looking for a second group to help deal with a particular threat.