Apple regularly makes iterations in the search algorithm on the App Store. Not a lot of people in the industry know how the App Store search algorithm works, or exactly what Apple considers when a search is made. But these seem to be the important factors:
1. App Title: While selecting a title for the application, it is extremely important to include keywords with the heaviest traffic. The keywords in the application title gets more weight-age than the other keywords.
2. App keywords: To improve the search ranking you need to know which keywords are relevant to your app and are used often by your target audience. New apps should focus on using keywords for which they can rank higher even though the traffic is lower for them. It is more beneficial to rank 25 for a keyword will a traffic level of 4/10 than rank 250 for a keyword with a traffic ranking of 7/10. Once the app gains more popularity then higher traffic keywords can be focused on.
PS - The space to add keywords is restricted to 100 characters.
3. Downloads: The number of downloads is extremely important to increase the search ranking on the App Store. Both daily and total number of dowloads determine the search ranking.
If you have a marketing budget, the best way to utilize it is by going for a burst campaign which will give you a boost in the number of organic downloads as well.
4. App Store Ratings & Reviews: The ratings and reviews directly impact the visibility and total number of downloads. Better reviews directly results into more downloads. As per a study, if two mobile apps have the same number of downloads, the app with the higher App Store rating will have a better search ranking.