The traditional approach
I'm with Abbot Amalric when it comes to In-app advertising these days, "Kill them all! God will know his own" - if I go to a web site or open an app that wants me to view an advert before I get to see the content then I quit.
But the problem is this is everywhere these days, American Express called me about a suspicious charge on my credit card yesterday, and when I called the number on the back of my card, they wanted me to listen to an advert for a health plan before talking to a representative - I hung up - it seems it's not that important to them.