I enjoy coding small projects that solve small problems that I come across. My Github is full of those, but I never seem to commit to one idea as I get bored or it reaches its limits.
How do you decide what to work on ?
Just having someone else use the thing brings it into the realm of reality way more than any technical factor.
I play music with some friends, mostly covers, and in all my time playing like this, there's been this constant band confusion that you might relate to if you've been in a hobby band:
What key do we play this in again? How long is the outro? Oh, you play the last chord in the verse for _two_ bars? Did anyone bring the chord sheet for that new song? Ugh, the 3G in the rehearsal space is so awful, and this chord site is so slow! Oh, did you guys learn the "acoustic" tab with the different chords? Etc etc.
So I started working on a little web app for sharing chord sheets with bandmates. Sure, we could just use a Dropbox with text files... But since it's a side project for fun, why not add some features?
Now it can parse a simple chord sheet format that represents timing, which most chord sheets neglect—so we can see that the last chord in the verse is two bars, and that the outro is eight bars... I learned about Service Workers in order to make it work perfectly offline... I used CouchDB/PouchDB for storage, which enables really nice real-time sync, and also works great offline... I learned how to make a nice print stylesheet...
And there are more coders in the band! So one guy implemented client-side chord transposing and changed my parser regexps into a proper grammar. An old musician/coder friend from my home town heard about it and is interested in participating, too...
And then I thought, hey, there's the new Web Audio APIs... so now it can also play songs with synthesized chords! And then I noticed that Chrome's latest release can actually compress and encode recorded audio, so now I'm imagining that you could record tracks in there, and share them, and do collaborative multitracking...
It's just growing like a living system, because it connects with something I and other people have actual desire for—and that's really fun!
Innovate on something that people do every single day. For example, people communicate every day, sleep, eat, exercise, work, entertain, use consumables. Make a list of literally anything you can think of that people do every day, and more than often ideas and issues to solve pop up.
LISTEN to people as they "wish upon things" every now and then. Ex. "I wish someone would xyz.. ", "I wish there was a way to xyz...", "When will there be xyz...". These types of comments are a goldmine for choosing a theme.
Hope I answered your question and that this helps, my friend!