Questions about advertising in applications as well as their promotion?

Question

Marketing

Now I plan to create the first competing application, a full-fledged one, so to speak, and there are several questions that I would like to clarify in advance.
1) With what services is it best to promote the application? What is the cost of promotion? AdSense?
2) How much does advertising in the application really bring from regular users/downloads? Which ad is the best? Again AdMob? What is better advertising in the application or buying virtual things / stickers / services .. which brings more income?

Answer 1

1. Depends on the application *
2. Depends on the application *
* - subject, etc.