How do you validate your ideas?

We all have plenty of ideas all the time, and we might be convinced that one of them will be really successful, so we start working on it. But maybe it's just what we think, and our thoughts don't match reality.

I know that, once you launch your product, you can ask for feedback from early adopters, but what do you do before launching? Do you use some specific tools to validate your idea or ask for feedback offline/online?

I'm curious to learn which strategies makers use!