Content for Cardboard should be "snackable virtual reality," said Jon Wiley, the product's principal designer, during the I/O developer conference on Friday.
"For Cardboard, you want [an experience] to be more like traditional YouTube content," he said, adding that Google's VR platform isn't really designed for "long duration experiences."
Google sees Cardboard as a device that friends can pass around to get a feel for what VR is all about, said Manuel Clement , a user experience designer on Google's virtual reality team. In that context, shorter content would work better.
While Google's rivals in VR and augmented reality have built polished, sleek headsets, don't expect Cardboard to get a high-end makeover any time soon.
"Part of the magic of Cardboard is the simplicity of the system," said Wiley, adding that Google may look to simplify the platform even more.
Although Cardboard is just a simple box with a plastic lens and a smartphone pushed inside, it can still provide a great experience if developers don't push beyond its limits, Wiley said. Developing apps that are too complex or sophisticated will exceed its capabilities.
To incorporate virtual reality into their apps, Google recommends developers start small and consider how introducing a 3D component will make their program better.
Allowing people to tour a house in 3D instead of just viewing a photo gallery would give a real estate app an advantage, said Erica Morse, a Cardboard user experience designer.
Developers must also remember that VR content can make people feel disoriented, so they need to take into account the physiological response to what people see, said Alex Faaborg, who works on the virtual reality design team. That means creating apps that allow the display and the person's body to work together.
Apps should maintain a stable horizon line, and head tracking needs to remain engaged so people can navigate environments smoothly. Uneven acceleration can lead to nausea, and if developers can't create seamless transitions, Faaborg suggests fading to black, or using audio to help with the transition to a new scene.
Some users might just hold Cardboard in front of their faces because they don't know they can move their head around to explore a virtual setting. To get people more engaged, developers could place an object off to the side so that users are encouraged to turn their gaze, he said.
And developers should think visually about displaying information, Faaborg said. If an app features a spaceship that's sustained heavy damage, don't use a bar graph to convey the information; show the damage on the ship's wing.
To help developers build VR apps, Google created Cardboard Design Studio, an app that explains both simple and advanced techniques.