At Pocket Gamer Connects London 2016, Nicholas Lovell, founder of GamesBrief, gave a talk on how to extend player sessions in your games.
"You've always got time to check Facebook, and Facebook's just a game," he said, and suggested that because of this, "your on-ramp has to be better than Facebook's."
Reel them back in
You can achieve this by implementing certain design features, such as daily tasks, which incentivise the player into returning to the game consistently.
Lovell also suggested letting players "potter around" in the game after having completed these tasks, so that players will want to continue playing even after they've completed their main "quest" that they set out to achieve.
You can see all our videos from Pocket Gamer Connects London 2016 in this YouTube Playlist.