If you are a first time developer, it is especially important to know which metrics you should focus on when you do your soft launch to do this properly. Here are the two which you should pay attention to:
Usability– I have come across new developers with ugly designs couple with horrible usability. You need to invest money and time getting the right designer as it is critical in getting important things such as an Apple feature, which can drive your app to succeed. To work on this, you can go to a site called usertesting.com where you can hire people to use your app and give you candid feedback.
Retention–what you would typically do is to do a soft launch in smaller countries which could replicate how the Western countries would react. This would drive lesser acquisition costs. Figure out what people are doing and how well they are retaining your app as this will be key on how well you monetize in the markets you are targeting.
One thing you should learn is to care about retention first as you will then figure out monetization, instead of the other way around.