Readdle's Denys Zhadanov has put together a good article detailing how Readdle launched PDF Expert for Mac (which Graham likes) and got to #1 in the Mac App Store. I particularly liked this bit on how they positioned the app in the research stage:
Many people told me that it doesn’t make sense to build a product that already has some decent alternatives. But honestly, I like competition. Healthy competition indicates that there is a good addressable market out there. Having a superior product that does things better and is differentiated enough can lead to a successful and sustainable business.
Thanks to our research and preparation, we were able to position PDF Expert for Mac really well. It steps in where Apple Preview is too basic and Adobe Acrobat is too cumbersome. With PDF Expert, people can actually do their PDF work much faster and easier, including reading, annotating, form filling, and signing documents.
As I argued on Connected last week, too many developers think that making a good app is all it takes to achieve "success". Preparation, research, and understanding the position of an app beforehand are just as essential. Denys has some other practical tips and fascinating stats, so make sure to check out his post.