Imagine, that your game works like the virus, so it feels the first condition of successful game. Is it enough to become popular on social games market? Unfortunately no, one time users do not earn many money (as much as you would like) and do not help you to get to the top-10 Facebook games. There is a good example for this case. It is a Flappy Bird game. The news about the game was like a virus. Everybody would like to try it, advice it to the friends, post to Facebook own results. But where is this game now?
This game has zero retention, because there was no reason to return the game. The game has no levels, no bonuses, no finite lives and even no game levels or variety of game characters. So, the game should convince the player return in a day or in a week. The next gold rule of the game tells about retention. Retention indicates how many players remain attached to the title over a certain period of time. Your players should fill the necessity to return to the game again and again. There is only one question what you should to do? The game should have as many variety of heroes, levels, combination as it is possible.
There is a list of most common retention examples.
1.user personal level
4.characters, which are the symbols of the game and help in the game
5.great amount of game levels (if there is in the ideology)
6.feeling of competition (possibility to get information about game-friends)
7.goals in the game(obvious, like in strategy games, or «collect 10 candy» as in King’s Sagas)
8.high scores list (friends list or the whole world list)
10.time-bombs (like the dragon house will be built in 2:00:00 hours or you will get a life in 29:50, timer is an integral part of it)
I put these methods in random order, so there is no connection between importance of advice and usefulness. First of all all the pop ups (for example Daily bonus or Goal) should be in game style. Wrong styled pop up can decrease the quantity of people who will interested in twice.
Whats about other retention method, such as user personal level, even King add user personal level in all their games. There is one more amazing idea. If you have a family game (when one game is similar to another one with different design and heroes, however the same mechanics), you can make a common level board.
Also, an interesting method to make the game retentive is to give users finite lives. It is a widespread strategy for returning users. If you will combine it with «Ask friends about life» it become even more effective.
The minimum you can do, make the game variable. For example create colorful heroes, additional items (like boosters, clothes for heroes etc). This depends on the game, but even in the trivia genre there is always a possibility to amaze the user.
So, retention, as for me, is the most complicated part of successful game creation. But it is not a secret that one time users never pay. Your game should have fans, which will return to the game and invite their friends. If you are not sure is your game retentive or not, check all 10 previous points. If you have all of of these points, you choose the right way or you are King game studio.