IMO These are the best way to rank App on Google play and App store.Select the right category for your app by looking the competition level,because in ASO app category placement is quite essential.Then Daily installations, driving more installs would have a great impact on ranking for your app.Then other key factor is your app’s ratings, that have a vital influence on your rankings in Google Play ,ratings and reviews are very strong signals Google play store.Finally involves in SEO as link building process and try to promote in social media for best rankings.