How could I increase my app's ranking in Google Play?

[JeanSharky]

Hi,everyone.

I'm a developer and have released my app in Google Play for several days.It's a VPN that belongs to Tool&Productivity Category.The competition is very furry and when I search some key words,my app stay too behind to find it.Therefore I want to ask about the method of ASO in Google Play or is there any professional and reliable company to do this?

This is my app in Google Play:https://play.google.com/store/apps/details?id=com.tbu.fastlemon.android_free

Please leave your good idea.Thank you all.