I want to share my experience in developing and selling my iOS application from the Productivity category. I will not tell about the application, so as not to be considered for advertising. Just graphics and conclusions that I drew.

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For 15 months, total sales of the application exceeded $ 29,000 and today amount to about
$ 2,000 per month ($ 65 / day). The total number of downloads has exceeded
500,000 , although most of them were received during the free distributions of the application.
The start was pretty good due to the fact that Apple placed the app in the promotional sections of New & Noteworthy and What's Hot in the American and Russian Appstores. This inspired further work, but subsequently the sales charts were not as spectacular. In total, the project has not yet paid for itself - about three times as much money is invested in the application. (The application was created by a team of two people. It took about 10 months to develop the first version.)
After the launch, the development bet was on various useful, though laborious, implementations in the hope that Apple would again pay attention to the application and fix it. We added cloud synchronization to the application (not via iCloud), localization into different languages, iPad-version and other features, however, this has hardly affected sales.
The biggest surge in sales of the application as it was, and remained at the time of the first appearance of the application in New & Noteworthy. The rest of the already smaller bursts were after the publication of reviews of the application on different sites and blogs. Attempts to advertise the application on Facebook and Google Adwords did not lead to any change in the sales schedule.
The main sales were in the Russian and American App Stores. The release of localized versions did not lead to fichering in local App Stores (in general, we localized the application in 12 languages, even taught the application to parse user input like this: 毎 年 12 月 20 日 ま で に ク リ ス マ ス プ レ ゼ ン ト の 準備).

Price
In addition to advertising on Google and Facebook, I experimented with the price and free distributions of the application. The price change from $ 0.99 to $ 3.99 did not have a significant impact on sales. Raise the price of the application - lower positions in the top charts, lower the price - the positions increase. Total sales are about the same.

The optimal price is determined depending on the number of visitors (traffic) who come to buy the application from outside Appstor.
Free distribution attracted attention to the application, but in general, this practice should not be used constantly and even more often. We spent about 4-5 free distributions of the application during the year. In the end, free distributions affected sales, there was a surge in downloads all the time, but the effect was less and less every time.
iPad version
After the release of the universal version of the application (version for iPad), sales increased by an average of one and a half times.
The iPad version was released just in time for the iPad mini release and shortly before the Christmas holidays, and Apple fixed the app on the small Makin 'a List promo list in the US and Canada. This slightly affected the sales of the application, but not at all as was the case with New & Noteworthy and What's Hot right after the launch.
Sales in Appstore after the release of the iPad version:

What's wrong?
Like many developers, I once represented Appstor as a kind of “gold mine”, which will make good money if you make a good product. He focused on other numbers in sales and on the fact that a self-sustaining project is not so difficult to do.
To understand the essence of the difficulty of making money in Appstore, you should think about the question: what, in fact, is Appstor’s task
for Apple ? This is an ecosystem that is aimed at the development and promotion of the entire iOS platform and the sale of new iOS devices. It’s not that users quickly find the right applications in Appstore (those who used the search inside Appstore will understand), but on the top of only a few dozen of the brightest and most attractive products. In a general sense, the beneficiary in Appstore is only Apple, and not a developer at all.
Therefore, it is somewhat naive to expect your application to be finished for being so useful, good, and neatly executed. In my opinion, this is how it was, and remains the most common misconception of developers regarding today's mobile applications. The editors of Appstore are not only monitoring the usefulness and uniqueness of the application, but also about how the application helps Apple develop the iOS platform, express its uniqueness, demonstrate how convenient and innovative the platform is. Blogs and websites that write app reviews act in much the same way. I didn’t work with Google Play and other platforms, but I think the situation is similar there.
By the way, our experience with getting into New & Noteworthy confirms this: the application was not captured after the release, but after it appeared in it as a function of reminders about tasks by location (geolocation) - just when Apple introduced this API in iOS 5.
I will be glad to answer your questions in the comments. Thanks for attention.
UPD: This is not an ad application. In this post, I just tried to answer the questions that I usually hear from friends when they ask "how is your application?"