The sheer amount of stuff I have stolen from IPs I know my players aren't familiar with

Building my homebrew world, I realized pretty early on that I belong to a few fandoms that I know my players aren't in. And let me tell you, this has been a HUGE help for me. It's like I'm already familiar with the mannerisms and attitudes of NPCs while doing minimal work.

I need a personality for an outgoing, boisterous tavernkeep? Well, that's Braum from League of Legends.

I need a mindbending puzzle? Yoinked straight from Outer Wilds.

I need sidequests for my players to complete in town for some extra coin? Sorry, Genshin Impact, those are mine now.

I need to design some beasties for interesting encounters? Legends of Runeterra has my back.

My players likely wouldn't even mind if they found out, but don't be afraid to reuse ideas from other pieces of media (as long as you're not profiting monetarily from it). It can go a LONG way into fleshing out the world you're building.