It depends on your aims and budgets.
First, you’d need to make a decent ASO which would include your Title and Description being optimized for the traffic keywords and the high quality Logo & Screenshots so people would actually want to installs your app from the rankings you’d achieve.
After that, you should run an incent installs campaign together with the reviews one.
And all these things you can do at one place: KeenMobi. They would promote your app for the lowest prices by providing real people installs, reviews, ratings, ASO and other cool bonuses.
100% Real People Reviews, Ratings and Installs
Custom Marketing Packages For Each Client
Free ASO Services (Title & Description Keyword Optimization)
Screenshots, Logo High Quality Redesign/Enhancement
If you are interested in any App Promotion services (installs/reviews/ratings/ASO/keyword installs), contact me at Skype: "keenmobi"