How should we cache user content? What's the best strategy?

hey everyone, i'm building this platform where people make tons of stuff, like posts, comments, and pictures. we need to get this content to users fast, but it's always changing and growing, you know. so, what are your best tricks for caching user content? are you doing client-side stuff, using a CDN, server-side caching, or maybe a combination? what have you noticed are the pros and cons of each, especially when the data gets old.