Have a set of NPCs who serve as mission-dispensers. Each of these has a very distinct tone to them, including a theme(-song). Players should choose one of these to accept a mission from, the mission should then have the characteristics and tone that the NPC presents. This way, your players learn that if they want an action themed evening (or next session etc.) they can choose by talking to the right NPC.
A simple example would be presenting the players a few different NPCs which they meet in short succession. The first NPC is carring a large weapon, has battlescars and maybe a prosthetic arm. When the players meet them in their secret hideout, weapons range or mercenary office, play a soundtrack from an action/hero movie. When the players accept a mission from this character, it will lead to action, shootouts, big explosions, high-speed chases and hanging-off-the-side-of-a-building scenes. The other NPC is someone mysterious, who doesn't show their face, their voice changes every few sentences, you hear whispers while they talk. They are met in a dark back-alley at night, speak to them through a divider that only shows a shadow, or "wears" a different body (though with an identifying sign) whenever met. Play a spy movie soundtrack or anything mysterious. Missions from this character will be about uncovering a mystery, being sucked into the middle of conspiracy, coming into close contact with the high and mighty, playing with danger. Scenes might include being ripped out of reality, meeting something from another dimension, infiltrating social gatherings of the high and mighty, only to find out something terrible.
Whatever your style, you can add your NPC with the characteristics that fit your storytelling! As an added bonus it also helps you focus on what kind of a story you want to tell. If those examples seem too restrictive/simplistic, add more nuance to the characters as you prefer.
- Make it clear to the players that they will have to choose before you introduce the characters, this will make them pay more attention and builds a small amount of tension
- If you want to play your next mission with one of a few types of themes, you can present the NPCs that represent these themes, this should also help you with planning/thinking ahead!
- If you want to give the players GM Choice on the theme, you can have an NPC that represents that.