What you are asking is similar to "I think I have learnt playing the keyboard well enough as an assistant in an orchestra, now how to create great music for ads or whatever to make some pocket money?".
This is a matter of creativity. The situation you describe is usually the other way around - people have ideas first and then learn whatever is necessary in order to realize their creativity, they don't start with a tool set and then look for ways to apply it. That is done by consultants. So may be you must become one?
Creativity can't be taught. No amount of tips is going to substitute for innate creativity, of any degree, because all tips are effective only when you have an idea to work with, which is the product of creativity. If you don't have it, in this case identifying a problem and imagining a suitable solution, just do what all/most successful companies do - copy, but add a tiny variation to claim that its different and your own.
All that said, my tip would be to keep eyes and mind open, and just build whatever you feel is right and release it. Do consider feedback but don't get discouraged by criticism. There are ample examples of how the most derided product ideas have ended up making quite a profit, not just in software, although luck had a major hand in their success.