I have been doing a lot of reading lately on how to grow a player base for my game(s).
The general consensus is that it is NOT easy, period. The second consensus that I keep reading is this: (I thought this version summed it up nicely)
16. Updates are not coming fast enough
Let us end with an easy one: social and multiplayer games need to be kept alive. If you want to retain users on the long run, you need to keep them busy or give them a reason to come back. Regular and substantial game updates, every 1 to 3 months, are key to staying in the mind of your users.
If your updates are slow, chances are your users will not only uninstall the game, but they might also forget to check it again later.