[jt2190]

  > don't really have any idea

First try and figure out what will motivate you enough to keep working on the app, and then pick an idea that fits with your motivation.

For example, I'm very motivated by user feedback, and I'm just not as interested in coding things that are just for myself or are hidden away on a server. So I tend to enjoy working on things that others will use, like user interfaces or APIs.

Things that I've seen motivate others are:

  * optimizing performance
  * making money
  * solving their own problems
  * working with large data sets
  * graphics and games
  * working with hardware
  * working with real-time data

You definitely don't need to come up with an original idea.