[retprogramisto]

What type of app/product?

You need to let users know why the app will be useful to them, what they can use the app for, and why your app is better/easier/faster/cheaper than their current solution. Infographics, Youtube videos, examples, reviews and customer stories can help here.

Maybe add referral bonus (referrers earn a percentage of sale profits, entry in giveaway, or app credits/coupons per active referred user)?

If there is any community/forum/social network for your app's market (e.g. Bitcointalk for crypto) you can advertise there. Likewise you could ask your market what type of platform/app would help them, then add those features to your app.