Index cards are a GM's best friend. Remember the Hipster PDA? I hate forgetting to give each player time in the spotlight. Therefore, I love having an index card for each player. I shuffle them before the game, and then flip the deck so I can see the top PC card.
On the left I put the information from the game system I need to be able to improv, things from the player's character sheet. I don't need numbers, just the background bits that help in roleplaying.
On the right side of the card I put the stuff the player loves to do in game with this PC. Play with his pet bear, drink at her regular watering hole, flirt with their favorite NPC, and so on.
I finish the left side with a question to myself. Has this PC gotten the spotlight yet? If not, I give them the spotlight ASAP, then put this card on the bottom of the deck and make sure the next PC gets a spotlight moment.
What's a spotlight moment? When you let the PC shine, make them the star of a scene. If they have a favorite action, like pick pocketing, flirting, or flying, I let them go for it. Action scene or pure roleplay, I make sure the character gets center stage.
Here's some examples. You can probably improve on these because no one knows your players better than you.
This is the Cypher System card. I have another question to myself: Has the PC had a GMI (Game Master Intrusion) yet? I'm talking a GM Intrustion that gives them experience points. The card helps me remember. GM Instrusions are fun, and players love the XP that comes with them.
This is the 13th Age card. When I'm working on a spotlight moment, I need the PC's One Unique Thing, their Icon Relationships, and their Backgrounds. Under the notes I might include favorite icon spirits and agents from past icon relationship rolls.
Here's the 5E card. What's important for spotlighting a 5E character might include the PC's background, trait, ideal, bond, and flaw.
Here's a generic GUMSHOE card. Drive and Occupation give me a handle for spotlight scenes.
I thought about doing a card for each GUMSHOE game, but realistically, I'd do them as needed for the games I'm running. On the right side I'd definitely list any sources of stability if they are used in this system, species for Ashen Stars, and so on...
It's easy enough to make your own for your favorite game system. They help me, maybe they'll help you.