Williamsburg is generally a safe city and common sense precautions should suffice to avoid trouble.  It has a low rate of crime and there are no particular spots to avoid, at night or otherwise.

Probably the greatest safety concern is driving on the local roads. The streets can be frustrating to navigate for a first-timer. Planning ahead with a map is generally good advice in Williamsburg, as many streets curve around and change names.  Fast drivers are not a prevalent danger in this city, but those paying more attention to their maps than the road can be.  Be aware of the low speed limits.  Many streets have speed limits of 25 mph, and those limits are enforced.  Also, areas along Richmond Road and Jamestown Road bordering the College of William and Mary have numerous crosswalks, and the pedestrians have the right-of-way.  It's a good idea to be cautious in those areas

There are also a few intersections that could potentially cause issues.  The most infamous of these is the intersection of Richmond Road, Jamestown Road, Boundary Street and the traffic-free Duke of Gloucester Street. It is located between Colonial Williamsburg and the campus of the College of William & Mary and it is a busy intersection to be aware of, due to its unusual traffic pattern, its busy pedestrian crosswalks, and its frequent fender benders.  The best advice for surviving it is to plan a route before getting in the car that avoids it altogether.  

The conjunction of Francis/Page/York/Lafayette Streets can be confusing as well.  This intersection now has a traffic light, which helps, but because of the way the intersection is put together, it is difficult to tell exactly which lane to be in and which way to turn, until you become more familiar with it.

For those seeking medical care.  Sentara Williamsburg Regional Medical Center is in the northern end of the city about 10 - 15 minutes from the historic district.  Now open, Riverside's Doctors Hospital is located off of Route 199.