If there is one area of your business to invest in, it's your culture. Culture drives employee engagement, leading to greater employee productivity and a stronger business overall.

But culture is an abstract concept that's difficult to define, and even more challenging to measure. Eighty-seven percent of organizations cite culture and engagement as one of their top challenges. With unclear metrics on the effect of culture on the bottom line, many companies are tempted to focus their efforts elsewhere.

However, while executives are unsure how to establish culture successfully, they are aware of its value. In fact, 91% of executives believe improving their company's culture would increase the company's value. Yet, only 15% of them say their company culture is where it needs to be.

That's why I set out to find out how top executives and human resources professionals establish a strong company culture and grow it. One of the top thought leaders on culture transformation, Hung Pham, is no stranger to struggles with culture.

Pham is the founder of Culture Summit, a conference that brings together hundreds of culture champions and thought leaders to share actionable insights and strategies on building culture from the bottom up. He founded the conference in 2014 to solve his own challenges with career disengagement.

Together, Pham and I worked to gather insights from HR leaders at top tech companies to understand what makes a great company culture, how executives can build it within their own teams and how to continue to grow that culture and improve over time. Here are five key takeaways from our research.

1. Focus on people

According to Janelle Gale, VP of HR at Facebook, "To scale company culture, you should focus first on your most important product - your people."

The people that make up your company are your most valuable resource. Yet, according to Gallup, only 32% of U.S. employees were engaged at work in 2015. You need to make sure your employees are the right fit for your team and feel like they belong to a community within your company, have what they need to thrive, and are focused on the success of your business.

For Facebook, this starts when a new employee comes on board. Gale says, "Each new person who joins the company goes through the same orientation program where they hear from our leaders and we tell them: this is your company now. This is a signature moment that connects every new employee to Facebook's mission, vision, values and culture."

2. Define your brand story

Your brand story is a powerful tool not just for attracting customers, but also for creating culture. A brand story shapes how your employees see the company and their place within it. It gives them a purpose for what they do.

"Employees want to be part of the story of your company - so you have to define that story through common language as you grow," says Dan Spaulding, VP of people & culture at Zillow Group. "Whether it is core values, company mission, or workplace norms, you have to intentionally make sure that people at all levels understand and embrace the concepts."

He adds, "They can't be words on a wall - they need to start every meeting, anchor business decisions and show up in your daily habits. Doing this well reminds your longtime employees of what they set out to do, and helps your new employees feel confident they know how to navigate your culture."

3. Establish a team mentality

Your culture brings all of your employees together and encourages them to think as a team, rather than as individuals. Especially when conflicts arise, it's important that everyone does what's best for the team and the company.

Tatyana Mamut, head of product at Amazon Web Services, believes having a common vision keeps top leaders aligned.

Of her own experience, she says, "We've needed to learn how to disagree productively and keep our teams moving forward in a unified way, even when our experiences and perspectives clash. No matter what our individual interests are, it's important to stay focused on a consistent culture in the face of fast growth, so the leadership has to have a unified vision and common set of values and principles."

4. Keep culture consistent

Change is inevitable, especially as companies grow and evolve. Your culture needs to be able to grow along with you. "While culture can and should be fluid, your company values should remain constant and consistent over the course of time," says Gina O'Reilly, COO at Nitro.

"Ultimately, your values will define your culture," she continues. "Since culture is the sum of how your employees behave, the right talent and team are crucial to shaping a positive culture. Rather than seeking good 'culture fit' during the hiring process, which can mean different things to different people, focus on how prospective candidates align with your core values in order to ensure you're making the best decisions for your business."

5. Prepare for growth

"The core of great culture is your values and the stories you tell," says Didier Elzinga, CEO at Culture Amp. "As you scale, one of the key things to do is make sure you actually listen to your people. Growing fast is really, really hard and can lead to what we call the 'Culture Crunch.' One of these effects is how people adjust to changes in the scope of their role as the organization changes."

Be prepared for things to change as your company grows and scales, and let your culture guide you and your employees through the transition. "You can't make your culture go up and to the right," says Elzinga, "but you can peer around the corner and see what challenges await you so you are better prepared for them."

How have you established culture within your own company? What has been its effect on your employees and your business? Share in the comments below: