Finding the keywords

Start with ten to fifteen terms a person would type to find an app like yours, not your app's name. Then search each one and write down the names and subtitles of the top three: the words they share are the words doing the ranking. The scan on an app's page does this for you, with what Apple's search box suggests after each term added on top, since those suggestions are what people actually type.

Cut by relevance first, then by the numbers: keep popularity 25 or more and difficulty under 60 where you can, and accept the best compromise where you cannot. Long-tail phrases ("daily habit tracker" rather than "habit tracker") have less demand and far less competition, and ranking for ten of them builds the downloads and ratings that later win the short one.

Before you change anything, mark the terms you already rank for: those bring the downloads you have, and a rewrite that drops them costs more than it gains. Keep a copy of your current name, subtitle and keyword field with the date, so any change can be undone in one release.

Then place: the term you most want in the name, the next in the subtitle, the rest as single words in the keyword field. Repeat the whole pass for each store you sell in; translated metadata is enough, the app itself does not need translating.