The following are design guidelines for designing visitor-facing museum technologies and tools, synthesized from the collective wisdom of the museum professionals we've interacted with.
1. Technology isn't the spotlight--technology should support and encourage the museum experience, not be the experience.
The museum experience is about the artifacts and stories behind the artifacts. If the visitor spends more time looking at their mobile device, etc. than with the artifacts, then the museum has failed.
2. Technology should be subtle enough that it doesn't get in the way of natural interactions.
Social interactions, conversations, etc. are part of what make the museum experience visceral. Technologies that demand the visitor's undivided, uninterrupted attention take away from that (e.g., headsets limit interaction with other visitors).
3. Structured experiences are good, but unstructured ones can sometimes be better.
Having a hierarchical, structured content organization might make it easy for navigation, but allowing a bit of room for messiness can facilitate serendipity.
4. Visitors often don't know what they want to see.
This is especially true for visitors who are new to a particular museum. Browsing is more useful than searching for most visitors, and also allows museums to suggest activities and things to see at the museum (physically or virtually).
5. Visitors want to know what they can see, right there, right now.
While putting everything from the museum's collection online or on an appliance/device has its uses, what most visitors are really interested in is what they can see at the museum. Frustration ensues when a visitor sees the object online, but can't find it in the museum.