There are several great tidbits in this article: http://www.mobileworldlive.com/tapjoy-identifies-attributes-1m-games

App monetisation player Tapjoy published a report detailing the key signs an app is on track to generate $1 million in revenueSome 84 per cent of apps with 1,000 or more users who completed three purchases within the first 83 days broke the $1 million barrier, with apps that had 4,000 users completing three buys hitting $1 million “100 per cent” of the time.

There you have it. Have 1,000+ users complete 3 in-app purchases within 83 days, and you’re on the road to success.

In order to hit the $1 million level, a 35 per cent conversion rate from first to third purchase was the “critical number”.And the bulk of in-app purchases also come from a few “best selling” items – in over 50 per cent of mobile games, the best-selling item is sold 20 times more than the worst selling. So in summary, get lots of users to purchase a few things in your app, have them play for a long time, and figure out the best selling items quickly. Easy!

My Apple Watch games Blackjack Mini and Berry Quest won’t have in-app purchases, so we’ll see what new lessons we pickup along this journey.