What are some ways to make a mobile game more sticky?
I have been benchmarking all the Zynga games to see all the things they do (Zynga poker, etc).
Although, if you look at Flappy Bird, it was so simple and pretty much the opposite, yet still so incredibly popular.
What are your tried and tested ways to make a mobile game more viral?
I don't have specific tactics for making a game more viral but Gabe Zichermann has a couple courses on Udemy about gamification.
Many of the lessons go into the psychology behind user behavior and there is a lot of insight that could trigger your own ideas. Understanding what motivates players is critical to creating experiences that are "sticky".
After going through the course you'll learn that there are essentially 4 types of people, Achievers, Socializers, Explorers, and Killers. You'll be able to see that Flappy Bird is triggering achiever's needs whereas Zynga is triggering a socializer's need. It's possible to satisfy multiple player types with different mechanisms.
Here's a paper from Bunchball on several gamification strategies: http://www.bunchball.com/sites/default/files/downloads/gamification101.pdf
Watch these two great talks by Gabe Zichermann given at Google:The Gamification Revolution: How Leaders Leverage Game Mechanics to Crush the Competition