In the world of mobile apps there are two major places where you can sell your products ‐ Google Play Store for Android apps and Apple App Store for iOS stuff. Both markets are really competitive, so if you want to be successful on either of them, you need to invest your time, effort and money not only in the development of a top notch app, but also in your store optimization and promotion.
If you are familiar with App Store Optimization (ASO) for Google Play Store, or with SEO in general, it won't be a completely new story for you. Apple App Store optimization is sort of similar to ASO for Google Play Store but due to the differences in the ranking algorithms, there are major differences in the optimization approaches, too.
Here are the major factors that make or break your good rankings at Apple App Store. Basically, there are 3 groups of factors you need to consider: keywords, visuals, and off-site factors.
While for Google Play Store many experts don't consider keywords to be of top importance (though many others dispute this approach), with Apple App Store (almost) everybody agrees keywords, in addition to the number of downloads, are the most important ranking factor.
This is so because the ranking algorithm used by Apple App Store isn't as sophisticated as the one used by Google Play Store ‐ in a sense Apple App Store is more like the search engines from decades ago when no complicated algorithms were used for rankings. Unfortunately, this opens the door to abuse. Needless to say, it won't help if you abuse the simplicity of the algorithm and stuff your pages with keywords.
Since you don't have a limitless text field for keywords, you need to be very picky which keywords to include. Quite naturally, keywords are most important in the title and the description, so pay special attention to these areas. It really helps, if you perform some A/B tests with these to find the winning combinations.
Very often your keywords come naturally, but sometimes you need to be more creative. For instance, if you are selling an app with lots of competition, you might have to think about minor keywords as well. You should start with the major keywords, but if this drives you nowhere, think a little about less competitive keywords as well.
You can use tools to give you ideas. There are many such tools. One of the good ones is this keyword tool.
If you are selling on local markets, don't forget to localize keywords as well. Localized keywords can make a huge difference for your popularity!
Visuals are frequently neglected by developers but they have a huge sales potential. As a rule, the more competitive your niche is, the more important visuals are. Visuals include stuff such as logos, screenshots, trailers, etc. Technically they are not part of the ranking algorithm, but their role is very important ‐ they attract users' attention and they do help for branding.
Your icon is the first (and frequently last) visual users see. This is why you need to put lots of effort in it. It's especially important you use the same icon everywhere in your app and on your pages. This consistency helps you big time to build brand recognition.
The same goes for the first two screenshots. Make them as nice and informative as possible. You might think that if your screenshots expose all your functionality this will lead to less downloads because users can see right away your app is not for them, but the logic is just the opposite. You don't trick users with vague screenshots just to make them increase the number of your downloads because even if you somehow manage to fool them, it's almost certain they will leave you a negative rating. A negative rating really hurts!
3 Off-site Factors
Finally, off-site factors are one more group of factors to consider. These can be tricky because they are somehow outside of your control. These factors include: number of downloads, as well as ratings and reviews.
In order to increase the number of downloads, you can write good descriptions that make users go the extra mile and download to see your app for themselves. However, with the fierce competition at the Apple App Store, many good descriptions go unnoticed, so don't expect miracles simply because your descriptions are perfect.
Your second option is paid promotion. You can use PPC, Facebook promotion, or traffic from other social networks/popular sites in order to bring users to your app and hope they download it. However, as you probably guess, getting a good number of downloads via paid promotion is everything but cheap.
The second off-site factor for good rankings at Apple App store are user ratings and reviews. What you need is favorable reviews, but these need to be authentic because otherwise they might do you more harm than good. However, don't pester users for reviews, though ‐ a single annoyed user can give you such a bad review and a low rating that it can literally kill your app. While it's great to have numerous positive reviews, it's much better to have no reviews at all, than to have bad reviews and low ratings from disgruntled users.
If you make the effort to optimize your App Store pages as described above, this seriously increases your chances to rank well there. Of course, even if your pages are superb (in your opinion, of course), this doesn't necessarily mean you will be successful, but it certainly makes it more likely. This is why when you launch a new app, you should always spend time to fine-tune its keywords, to make its visuals appealing and to promote downloads, ratings and reviews (in an unobtrusive manner). If your app itself is good, it's quite possible you will see good results.