As November 2017:

Ad Networks:
We see the Apple Search Ads being quite good, Facebook is the standard for getting high quality downloads. For Admob and other networks, you need to know them very well to drive quality downloads for good prices.

App Store Optimisation:

We have seen Apple doing big changes this year, making it more difficult for newcomers; while giving established apps more reach. It will be interesting to see how this evolves. For sure there will be many opportunities here. I would be happy to chat with you about this topic with you in a call.