When you consider there are collectively more than 2.4 million apps in Google Play and Apple's App Store, landing on any kind of "top" or "best" list is a remarkable feat. But just how does a developer do it?

Jamie Davies, general manager of Zynga's FarmVille 2: Country Escape, has some advice. In April, after launching the Farmville franchise's first mobile-only app that can also be played offline, the game was named "Editor's Choice" by Apple in 155 countries and designated by Google as a top tier app in 71 countries. Within the first six days of launching the game garnered more than 4 million downloads and across the Apple platform has reached the number one "Top Free App" in 20 countries, the number one "Top Free Game" in 40 countries while also breaking into the "Top 20 Grossing" chart in the U.S.

The original Farmville web game recently passed the five-year milestone so Zynga has had plenty of time to figure out what works and what doesn't. At the same time, Davies says it was important to think carefully about what new, fresh experiences Farmville fans would want on mobile given their expectations of the overall brand. The question, she says, became "What do we need to do to maintain and deliver on that brand promise, but make something new and different." Here's her advice for building a massively popular app.

Think carefully about session length.

Players of Farmville games on the web can spend hours managing their farms but mobile users often use games in smaller bites, such as while waiting in line. Zynga wanted to make sure players could pop into the game for just a minute as well as for longer immersive stretches. "Everyone's very busy these days and you only have so much time to take a break out of your day, so we wanted Farmville 2: County Escape to be able to account for a two-minute break or a two-hour break," Davies says.

Understand the importance of emotional connection.

If you're going to break through the millions of apps vying for the attention of consumers your app needs to connect emotionally with users so they want to come back. You can achieve this engagement through subtle design effects, such as the art employed when someone makes it the next level. "It's the eyes of the cows when they're ready to harvest milk. They're looking up at you as if they're making eye contact, and responding when you tap or when you touch the screen," Davies says. "So [it's] understanding the devices and the form factors through which consumers will be experiencing your app and making sure there's delight and emotional activity when they tap on their farm."

Jump start the first use.

What users experience the first time they try your app is paramount. The first-time user experience in Farmville 2: County Escape includes a series of brief tutorials that make a person feel like she's playing right away while giving tips and tools that help her know how to play. "Make sure that you get players quickly through that experience so they know what to do next and that they very early on have a positive association and connection with the game," she says.

Prioritize accessibility.

The most popular apps are often ones that are accessible and digestible in a way that doesn't feel intimidating. "So, it's really thinking about balance. You can certainly come to the game and figure out, 'Wow, if I'm strategic and carefully plan my next move I can maximize my progress,' or you can also just come in and be successful and make progress by enjoying what you're doing in tending your crops, in crafting goods and taking care of the animals," she says.

Offer single-player mode.

Farmville has traditionally been a social game people play through Facebook but with Farmville 2: County Escape Zynga wanted to give users the option to play autonomously. "Social control and choice is really important, because some people want to play with 100 friends and some people want to play with their two best friends and some people want to play on their own," Davies says. "So making sure it's a satisfying experience no matter which avenue a player takes has been critical to the design of the game." (Click here to ready why another developer says single-player option is the new necessity.)

Stay true to your audience.

When designing an app it's easy to concentrate on delivering new features and content, but if you have an established brand such as Farmville it's equally important to continue to deliver an experience users expect. "That doesn't mean we won't innovate and deliver things that they would never have expected or surprise them in a great way, but I think you can easily go down the path of catering to a different audience," she says. "At all times we come back to who's your audience and what are they going to think of this feature or a new experience that we're planning to implement in the game."

Quickly react to user feedback.

Players appreciate when a developer quickly incorporates their input, feedback and suggestions. So, while you might have a long-term vision for your app, if you stay on a path without stopping to listen to customers regarding what they want you can easily go in the wrong direction. "It may seem obvious but I think it's easy to become set on plans that you make, so you have to be willing to even disrupt your own strategies and your own plans because consumers may be thinking about it differently."