You can promote your app by writing press release, App Review Submission,Classifieds Submission also can submit video of your app on different video submission sites..Feature the App in an Official Blog.here are some links for your reference....
1. Leverage Your Mobile Website
2. Feature the App in an Official Blog
3. Focus on Emails
4. Create a Demo Video
5. Consider Alterative App Stores
6. Apply for Awards
7. SEO Matters Here
8. Join Developers & Entrepreneurs Groups on Social Media