Stop thinking about new ideas and start getting deeper in the first thing that comes to your mind. Iterate through it, don't develop yet. Be at least one/two weeks thinking only about it, Can it be extrapolated to something else?, How would you do it?, Improve it in your mind, iterate few times, find which niche could fit. Start implementing it... and iterate again, and again.

After a few weeks you will get a deep understanding on it... ideas will flow.