Building a superstar team is a mixture of art and science. As Google's Project Aristotle taught us, hiring a team of all-stars is not necessarily the surest route to success. In their efforts to crack the code on team effectiveness, Google's researchers discovered that the real magic lies in some key characteristics and intangible factors such as dependability, structure, and -- most important -- psychological safety.

When everyone on a team feels safe to offer up ideas, take risks, and ask questions, teams become something more than the sum of their parts. It's important to remember that a group of workers does not a team make. Real teams collaborate and work together for a common purpose. Therefore, you need to consider more than the skills employees bring when adding them to a team.

How well do team members work with others? What motivates them? Do they view their co-workers as allies in a common cause or as competitors in the quest for advancement? As a leader, you also need to nurture your team members as they develop, encouraging the group norms that lead to creative and cooperative groups. Here's how:

1. Build trust.

Psychological safety makes team members feel comfortable taking risks, asking for help when they need it, admitting mistakes when they occur, and providing and receiving constructive feedback. Trust is how you get there. In the workplace, trust is built over time, as employees rack up positive or negative experiences. Trust is also built when employees can identify with their teammates through shared experiences or getting to know one another on a personal level.

As a leader, perhaps the most effective way to build trust is to model vulnerability so your teams can see it's OK to be human. Take Uber CEO Dara Khosrowshahi: When he left Expedia to take the helm at Uber, he admitted feeling fear in his parting memo.

Another way to show vulnerability is to admit your own areas of weakness and ask for constructive feedback. Mark Daoust, president and CEO of Quiet Light Brokerage, recalls a time he did this at his company. "We held a voluntary brainstorm session to address some areas that I was struggling with. All of our team showed up and provided invaluable insights on problems, along with actionable solutions," he says. By opening up, Daoust was able to elicit valuable contributions from his team.

Practicing vulnerability is never easy, but the resulting boost in trust is well worth any initial feelings of discomfort. Without trust, instead of collaboration and bold new ideas, you'll get hidden agendas and political maneuvering, unhappy employees, and ineffective teams.

2. Give your employees a well-stocked toolbox.

When your employees have the right tools and training to succeed, they'll feel connected to their work, able to make real contributions, and empowered to offer up new ideas. 

Make sure your teams can communicate easily and informally with tools such as Slack or Chanty. And while a digital asset management system will give your marketers one place to go to manage, share, and distribute marketing collateral, integrating it with tools like Office 365 and Hootsuite will turn a DAM system into a companywide collaboration platform. If your employees work remotely or are constantly on the go, reconfigure tools for mobility so they can remain efficient and effective outside the office.

Training is another important toolbox component. Beyond making employees stronger team assets, training can also persuade them to stick around longer. A 2018 Bridge survey found that Millennials, the largest generation in the U.S. workforce, are more likely to stick with jobs that offer development opportunities. Most companies use an integrated learning management system for training; other e-learning platforms (e.g., Udemy, Khan Academy), mobile apps, and podcasting can also prove useful. Short video-based content is another option especially suited to the packed schedules of the modern worker.

3. Develop goals that strike a balance.

As a leader, you want to set goals that achieve a balance between ambition and reality. Godard Abel, CEO and co-founder of G2, a software review platform, says that his company sets goals for its sales reps that they can realistically expect to hit about two-thirds of the time. "That's a good way to really stretch and challenge yourself," he explains. "It is that balance of enough challenge but not so much challenge that it becomes demoralizing."

Finding the balance that motivates your team members to stretch without leaving them feeling defeated at every turn is notoriously difficult. One common error is setting too many stretch goals at once. Tesla, for example, has famously failed to meet many of founder Elon Musk's ambitious goals, leading to widespread market skepticism.

To set stretch goals that make sense, first consider recent company performance. If your numbers are down, it may not be the best time to challenge your teams -- research has shown that bold action is best taken during periods of strong performance. Toyota, for example, was able to reach its stretch goals for fuel efficiency on the Prius during a period of growth, when slack resources were available for the development team to rapidly execute on the challenge.

Building a successful team requires more than hiring people with the right skill sets. You also need to foster psychological safety so teams feel comfortable taking risks, dreaming up new ideas, and tackling stretch goals. As a leader, you can help by fostering trust, giving your teams the tools they need to succeed, and setting appropriately ambitious goals.