Promoting an app needs some knowledge to have a good performance. In addition, it is good to know that there are some ad networks like IronSource or google ads which your app can promote per each install. In other words, you will pay those networks, when they install your app. It can vary from $ 0.001 to 1$ per install depending on your app keywords and category. That's why we always mention that you should choose a right app category based on your budget and idea.
It's always better to do a continuous advertising instead of setting a high budget for a short period of time. The apps are growing during the time. So just leave your app advertisement responsibility to us and be patient to see the result.