You’ve collected some ideas? Now it’s time for the second part.
Firstly, you should work out the details of your favorite idea. Draw some sketches, note down some cool features. Generally, think about it.

Secondly, check if somebody already implemented your idea. You can use Google or any other search engine. Sometimes a view at uspto.gov can be useful. So, what’s your outcome?

Somebody has already implemented your idea: You should be depressed. Yes. No, of course not. This is rather a good sign than a bad one. You know that there’s a market, there’s interest. But it doesn’t help if your current idea is very similar, perhaps the same, as the existing one. “What can be improved?” That’s the essential question.

Nobody has implemented your idea: Before you start implementing your idea, ask yourself: “Why haven’t someone implemented this idea yet?“. Maybe it’s so worse, that there’s no market or interest. Or somebody implemented it unsuccessfully. Remember: It’s harder to introduce a new concept than go with an established one.