Ever want to make an NPC that the players connect with? That they find interesting? Here's a technique that works for me. I use it sparingly. I let the players design the NPC.
Not the stats, not the role the NPC fits in. I've got that covered. I go around the table and ask them in turn to tell me something about the NPC. I'm still the GM so if they go way silly or something that won't work, I will gently modify or ask for another idea. Usually one circuit around the table is enough.
I give them the NPC and say, tell me about ________. They tell me something. I say "It is known" and write it down. Then I ask the next player. It's a little like the Montage technique.
EXAMPLE: As a hook, I had Opal's sister Sapphire get captured by devil cultists and thrown into the gates of hell. Opal is a PC, Sapphire is an NPC I just made up. The woman playing Opal was excited by this idea, but we didn't know anything about Sapphire.
So I asked each player, "Tell me about Sapphire, what do you know?" Opal should know her sister -- for the others, I said "You've been traveling with Opal for quite some time. She's told you stories about her sister, what stuck in your mind?"
Player: "She has Blue Hair." GM: "It is known."
Player: "She has a penchant for losing things, even things she's not touching. Things near her just go missing." GM: "It is known."
Player: "She's a cliff diver. The cliffs in her hometown have low gravity, so she can do lots of tricks on the way down." GM: "It is known."
Player: "Her eyes match her hair." GM: "It is known."
Player: "She can alter reality with her thoughts. Only little things. A door is slightly to the right of where it was before. The blue fork is now red." GM: "It is known."
You get the idea. I now have a very interesting NPC who needs to be rescued from hell and the players know Sapphire way better than me telling them what they remember about Opal's sister.
This example comes from a recent Numenera game where weird is the new normal, in a more conventional game you might keep things more "realistic."