Having a background in mobile advertising, I agree with your point #3 entirely.
The worst would be when you're in the middle of a video and an ad just randomly covers your entire screen.
Point here is that ads are annoying and distracting, but if you gotta do it for monetization purposes, put it where it's the least intrusive and will cause the least disrupt to user experience.
RE: 6 Dont's for Beginner App Developers