DO NOT buy installs or reviews from anyone, because that will only hurt your rankings and revenue.
3 of my apps rank first for direct keywords and get 300-500 installs per day. To achieve this, I follow this rules:
Firstly, app name (package name too) has to include exact keyword that you're targeting.
Secondly, description should be long and meaningful, with keywords in sentences. Also try to make it as catching as you can and add a call to action (example: PLAY NOW and enjoy this crazy game, which will keep you wondering for hours!).
Add atleast 5 screenshots (+for tablet, TV and wearables if suitable), also make sure to add a promotional video ($5 on Fiverr).
Depending on your budget, you should use AdWords campaigns to advertise the game for the first few weeks. Yes, AdWords, because they help with ranking more than other advertising companies.
After that, you should see a big increasement in ranking and thus downloads + revenue. If you don't get high rankings (at least top 10, depending on keywords), you're doing something wrong or your app is bad.
If you'll have any questions, feel free to PM me.