Build a great app but don't forget about marketing
Whatever type of product you decide to build, you need to make sure it's something you're interested in, something you care deeply about. Don't build it if you're not passionate about the idea or possibilities it holds, don't build it because you think there's a gap in the market and it'll make you millions because it won't.
Build it for the fun of doing it, build it because you're passionate about making great products, build it because you enjoy the process, build it for any other reason than to get rich.
Making a living from building and selling apps is bloody hard work. Most apps fail to make a return on the cost of development, let alone sustain a lifestyle. The chance of failure is very high and the odds stacked against you. If you followed your passion and your app does fail, at least you'll have shipped something that you can be proud of.
Building and shipping a great app is not all you need to worry about. There's also this other thing called marketing. As creators, designers, and builders we often try to ignore it. We tell ourselves marketing is not real work and our product is so great there's no way it can fail, it'll all be just fine. Well, guess what? it won't.
I know a lot of people hate marketing because of its sleazy image. But marketing doesn't need to be sleazy and doesn't need to cost anything, but you do need to do it. Good marketing is about getting people interested in your product before it's even shipped, it's about building hype, building a following of people eager to use and try your app. It's about being smart, tipping the odds in your favour and not leaving things to chance.
The worst thing you can do is throw your app up on the App Store and hope for the best. You need to build a great app and have a solid launch plan in place, this is the only way to win in the App Store. If you don’t have either you’re setting yourself up for failure.