looking for the better way how to promote my App

What do you mean by "better way"? Better than what? What did you try and what did you know about promotion?

For free you can share it on forums (android specific or like on reddit).

If you can spend some money:

• use AdWords to show ad
• find sites related to your app using some rank (like Alexa) and send emails to them. Ask about writing article about your app or you can order ad on these sites
• use some service to perform previous step faster (like ispreadnews com but I didn't use this one)

1. Build a microsite.

2. Build a teaser website.

3. Start a blog.

4. Share your content.

5. Create a product video.

6. Pitch to app review websites.

7. Contact bloggers who would care.

8. Apply for awards.

9. Always be collecting emails.

10. Post on Pinterest.

11. Manually recruit customers.

12. Run a contest.

13. Create a Facebook group.

14. Take advantage of voicemail.

15. Make good use of App Store Optimization.

16. Contact admins of related Facebook pages.

17. Optimize your email signature.

18. Consider offering a promotional price.

Here are some sites/forums where you can create a post about your app

• reddit.com/r/androidapps/
• android.net/forum/android-apps/
• forum.xda-developers.com/
• forums.androidcentral.com/android-apps/
• androidforums.com/forums/android-applications.4/
• android-zone.ws/forum/2-android-applications/

There are some free tips to promote your app:

(1)social media: you can advertise your app in some social media, like Facebook,Instagram. Adding some friends about app developer to share the experience and idea with them. Of course, you can reply relevant post and add new post in some forum to advertise your app, remembering put your app link in your reply.

(2)content marking: by writing blogs and essays to introduce your app, raising the publicity of your app.

(3)cross promotion: if you have published more apps that have received good responses, you can use the platform completely to advertise your app, because the potential audiences are the precious resources for your new app.

(4) special website: you can put your app on some special websites, like classified sites and review sites. The installs will increased when audience browse these websites.

(5)app store optimization: optimize the name, icon, description and screenshots is a good way to promote your app. Create an appealing and attractive icon and name is useful for you, and add the keywords in your app title and description can increase the search ranking of your app. Indeed, you can add the reviews' screenshots to show the real response of the users.

(6)introduce to friends and relatives: you can share your app to your friends and relatives to increase the installs of your app.

optimizing app have many ways to do except the free promotion. If you want to get more effective return, you could try the paid promotion. Please contact me if you are interested in it.
email:business@reviewapp4u.com

Pleasure!