HTC's support website has a safety guide for using the HTC Vive. You should read it and follow it. Seriously.

Carefully read and follow the Safety and Regulatory Guide provided with your HTC Vive before installing and using this software.

A portion of the Safety and Regulatory Guide, available from HTC's support web site, is reprinted below to provide you with an example of some of the safety procedures recommended by HTC. This is not the complete guide, you should read all of the guide from HTC. Please consult HTC's web site for the very latest information. As stated in the HTC Safety and Regulatory Guide, provided with your HTC Vive:

Ensure the Area Around You is Safe for Use of the Product
While wearing the product’s headset you are blind to the world around you. The image displayed in the headset
will not match the real world. Always use the product in a clear and safe area. Do not rely on the product’s
chaperone system for protection. Do not use near stairways, large windows, heat sources, or outdoors. Clear the
play area of people, furniture, and other things that may be obstacles or block you from freely moving around.
For example, if a pet comes into the room while you are using the product, you likely will not be aware of the
pet’s presence and you could trip over your pet while moving in the virtual reality environment.

It is recommended that the product be used only while under the supervision of another person who is ready to
warn of hazards that may arise while the product is being used. Examples of hazards that could arise include, but
are not limited to, tangling of a cable in a manner that presents a tripping hazard, pets entering the area where
the product is being used, and the user walking too close to a wall or another hazard).

Be Aware of the Cable and Connections
Keep in mind the location of the cable and connections running from the headset so that you are not likely
to trip over or pull on them while moving around or walking around the play area. Move your feet slowly and
carefully to avoid tripping, including on the cable. Make sure to maintain good footing. Tripping over the cable
or contacting obstacles could cause injury or damage.

Take Care of the Controllers
While using the hand controllers, always check that you have sufficient overhead and surrounding clearance
to allow you to fully extend your arms outward and upwards. Hitting persons or objects may cause injury or
damage. Hold the controllers firmly and always use the wrist straps. If released while using, the controller may
cause injury or damage.