My Mobile App is for Business Travelers, Tourists & Locals.
The first step is to create a landing page and a blog section.
Any PR/communication/sharing you do should link back to the blogpost on your own domain.
Also, make sure to capture potential early adopters.
Post regular updates regarding your development (if you have a well-defined roadmap) and engage user feedback on specific forums.
If you need more details it strongly depend son your product/target.
