Lead with your niche keywords. Put the lowest-competition terms above closer to the start of your title (Apple weighs the first 25 characters most heavily).
Use medium-tier keywords in subtitles + descriptions. They have enough search volume to drive installs but still rankable.
Avoid stacking too many high-competition terms. Generic words like "tracker" or "fitness" rarely rank without massive download history.
Iterate every 30 days. Use this tool to re-check your competitor's keyword set as the market shifts.