Hi,
year ago, i used pretty good keywords analytics website for Google play and iTune, but i forget website name. So please suggest me some good website if you know or you use 
You can use Google keyword planner and Keyword tool.io to have the best research for your seo project
How to Find the Right Keywords - tools
Luckily, there is no need for you to guess your keywords. Keyword tools will help you to find amount of relevant keywords. There is a simple way to find what are the most popular keywords related to the topic of your app. Here is a list of the top platforms mostly used:
App Annie
MobileDevHQ
AppTweak
Sensor Tower
SearchMan
Mobile Action
Appcodes
Gummicube
App Mind
These tools aims at helping you to find out the keywords you need, figure out some of your competitors’ keywords and suggest you new ones and more. Like we search something on Google, you’ll see the list of suggested/related terms when you type your query on App Store search bar. You can tap on any of those suggestions to quickly perform the search. Do your research on which tools fit your needs and budgets, and then see which ones work best for you.
Each keyword tool will have its own advantages for measuring competition and searches. Keep patient and make full use of them. Keyword research will help your apps identify with a wide range of potential opportunities to attract more installs and drive more traffic.
There are many keywords tool available for app store and play store keyword analysis like:
Google keyword planner
Google trends
App Annie
SensorTower
Apptrace
AppMonsta
AppTweak
SearchMan
Mobile Action