cache invalidation strategies, what's your go-to?

We've all been there, right? You put in a caching layer and then waste ages fighting with cache invalidation. It's so easy to mess up and end up with old data. I've tried TTL, event-driven stuff, and write-through. What works best for you in different situations? Do you have a go-to strategy, or is it always a case-by-case thing depending on how quickly your data changes and how you read and write it?