It's hard to think of something I wish I knew earlier tbh. Svelte (and SvelteKit) are just so simple and approachable that I feel like whenever I need to do something new I can just try what feels most intuitive and it just works. I've heard the same thing from a lot of other people too. If anything I would just keep an eye on reactive statements; I wouldn't trade them for the world but they can be dangerous if you don't keep an eye on them.