The number of social games that exist today is staggering. facebook alone has over 10,000 game apps. Still, only 20 facebook games have more than one million daily active users (DAU). Why are so few successful? To find out, we looked at the 25 largest social games as well as the fastest growing newcomers. We wanted to understand what the best have in common and which features have the highest impact on monetization, virality and stickiness. What we found was quite surprising. Here is our top 10 list:

#10 Daily Bonuses: The best apps reward players for coming back. A simple way is to reward daily login and increase it each consecutive day. What works even better is to add an element of chance like a slot machine. A great example is the daily spin in Bejeweled Blitz. There players get a daily coins reward, a consecutive days bonus, a random spin, and even a viral incentive (the more friends you have the more bonus). When PopCap introduced this in July 2010 it increased DAU by 60%.

#9 Cuteness: Another trick is to exploit human instinct to protect and nurture. Simply show players a cute puppy with large baby eyes and few can resist. People have to click and pet it – and show it to their friends. The best way is to combine it with a viral dynamic as in the baby whale example from Happy Island. When CrowdStar introduced this in January 2010 it generated tons of feed posts and free viral installs.

#8 Appointment Dynamics: Some features require players to return at predefined times in order to get rewarded or avoid punishment. The classic example is harvesting and withering, which was first seen in Happy Farm in 2008. Many city simulation games like Millionaire City also use this. Players rent out buildings and must come back on time to collect rent to avoid losing it. Appointment schedules combined with loss avoidance and rewards are a strong psychological incentive.

#7 Boosts: In contrast to decorations, boosts are virtual items that give players a functional advantage. That could be extra time, a tool for faster harvesting, or items that increase health. Boosts are one of the best drivers for monetization. A good example are the multipliers and color bombs in Bubble Speed. The trick is never to give unlimited boosts but consumables that deplete over time.

#6 Energy: Some apps limit how far players can advance in each session through scarce resources, such as energy or lives. Then they sell refills that let users advance more rapidly and save time. Energy was first seen in Metamoki’s Mob Wars and today is the core monetization driver of most Zynga apps. Even poker apps use it in the form of chips. However, it can be a double edged sword. If you limit resources too much, users get annoyed and churn increases.

#5 Achievements: Rewarding players with virtual badges can significantly increase stickiness. What works best to direct gameplay with quests (players get explicit tasks). When Mafia Wars introduced achievements in April 2009 their stickiness ratio (DAU/MAU) increased from 23% to 25%. Not surprisingly, Zynga also added ribbons to FarmVille and stickiness increased from 33% to 37%. Some apps even use quests for cross-promotion. For example, in order to get the rare bowie knife in Mafia Wars, players have to solve a quest in FrontierVille.

#4 Friend Interactions: The best apps increase retention by encouraging players to interact and re-engage their friends. Brilliant examples are the franchises in CityVille and the neighbor visits in FrontierVille. Players collect coins, XP and hearts for visiting their friends‘ homesteads. An even more effective friend interaction is gifting because of its reciprocity. Players feel obliged to send a gift back. This creates a endless loop and is also viral – the more friends players have, the more gifts they can send and receive.

#3 Staffing: The most viral mechanic makes players “hire” friends to get benefits in the game. A basic example is Baking Life. Here players have virtual temp workers in their bakery who cost in-game currency. Alternatively, they can hire friends – who work for free. The crew mechanic in mafia games is even smarter because benefits accumulate: Players get more power if more friends join their crew. The increase even depends on each friend’s strength, which makes this truly social.

#2 Crafting: The most engaging apps let players transform less valuable resources into more valuable resources by investing time, skill, money, or the help of friends. A great example is the horse stable in FarmVille. To complete the building players need to collect virtual items that can be found, gifted from friends, or bought. When Zynga introduced this it increased DAU by 20%, one the biggest gains from a single new feature. There are many variations of crafting, for example the weapons depot in Mafia Wars and the factories in CityVille.

#1 Limited Offers: The best monetization driver of all is to use merchandizing and smart marketing. An example is Texas HoldEm Poker. When users leave the payment flow without buying, a popup offers them a 24 hour discount. This alone can increase revenues by 10-20% through increasing the number of paying users. Even more powerful are limited edition items, typically around holidays like Halloween or St. Patrick’s Day. It makes people buy, who usually don’t buy. And it makes people who usually buy, buy more. The downside is that it requires ongoing fresh content. But since we are talking about virtual goods it scales the larger your app becomes.

Will these 10 mechanics turn every app into a blockbuster? Probably not. No trick in the world can make up for a boring game experience. So the biggest success factor of all is to get the underlying gameplay right in the first place.

About the author: Michael Kalkowski is co-founder and creative director of GameDuell, a global cross-platform social games community. Founded in 2003, they have developed more than 60 games for their own brand website, social networks, and mobile. GameDuell has a team of 170 people with offices in Berlin, Asia and San Francisco and is currently offering over 30 jobs, such as product managers and game designers.