A common pattern among the computer science crowd is the desire to find a gap in the market. We've seen people like Mark Zuckerberg receive the same knowledge that we have, and turn that knowledge into money. Many people I know of have gone through approximately the same progression that I did in terms of becoming dissatisfied with academia for being too impractical (is anyone actually going to read that thesis?), followed by becoming dissatisfied with industry for being too uninspiring (yay, I fixed that unit test. Again). These people then start looking for gaps in the market -- waiting for that One Great Idea (tm) to come down from above and strike them between the eyes.
The first thing to realise is that ideas are worthless. As many people have noted, there is no market for ideas, and this is for good reason. They're not worth anything. You can patent an invention, but not a startup idea. Your idea might be good, but it's not going to make money on its own. Your product might be OK, but it's not going to make money unless it's polished and marketed. And as a single developer working on your weekends, you're unlikely to be able to build anything reliable that's also easy to use and which solves an actual problem. And then tell people about it.
Now that we have that out of the way, ideas are still important. And ideas are fun. I have notebooks full of ideas -- some of them I've shared with others for feedback. A select few are in the process of being transformed into code in private git repositories. I enjoy playing around with ideas, even if it's good to keep a healthy scepticism on how successful they'll become.
A good shortcut for finding more interesting ideas than those of other people is through the concept of 'meta'. A meta-thought is a thought about thoughts -- i.e. one of the things that we believe makes us better than the apes. Metadata is data that we keep about other data -- think of that "last modified" column in your file explorer. That's data. Your files are also data. So it's data which is describing data. Wow. Inception. Metaception. Mind == Blown.
But more seriously, as you listen to other people's ideas, try to see a layer behind their idea. Or if you are thinking of an idea, look for the idea behind that. Three quick examples will hopefully clarify this:
People are creating startups. Most of them fail. Some smart people avoid failure by creating startup incubators instead of startups. They buy some cheap warehouse space and offer internet, coffee, and 'mentorship' to other people who want to run a startup. Most of the startups themselves fail, but they still pay their fees to the incubator. And the few that are successful also give a percentage of their shares to the incubator. The incubator isn't hurt by the failures and makes a fortune out of the successes -- all through taking other people's ideas one layer of meta deeper.
People are playing on the stock market and buying crypto-currencies. Some of them make a lot of money and write about their successes to encourage others to try the same. Many others are losing all their money -- they tend to be a bit quieter and keep their heads down. No-one likes talking about them. The people in the game who are reliably making money are either the stock markets themselves (Wall Street is worth a bit), or the ones who are selling data, books, code, and tutorials to the people who want to gamble their money directly. Again, these people are making money on others' successes and not losing it on their failures.
In non-tech circles, people still make money by proofreading, though not very much. If you are part of the minority that has a good understanding of the grammar of your native language, it's easy enough to find clients who are a bit bewildered by exactly how commas and apostrophes work, and who have read the distinction between effect and affect several times and have given up trying to work out when to use which. However the hourly rate for proofreading tends to be pretty miserable. I once attended a three day proofreading course though, and paid the single instructor several thousand ZAR for the privilege. I was one of dozens of people to do so, and the instructor made more money in three days using his proofreading knowledge than many of the attendees would make in their lifetimes with the same knowledge.
Of course, once you start doing this, you might never stop. What about a startup incubator that trains other people to create startup incubators? Or someone who teaches people who to teach? Or someone who writes blog posts like this one? Be careful of the rabbit hole, Alice. People who go down do not always re-emerge.