Physical therapy should include strengthening and endurance exercise for the neck and upper back. These are more helpful than stretching. Benefit will be only temporary if not done regularly. Manipulation by a physical therapist or chiropractor may also have benefit when combined with strengthening exercises. Body mechanics training at home, work, and during recreation is shown to be beneficial also.
In most cases you should avoid bracing or collars. The most useful drugs are anti-inflammatories, opiods (narcotics), and muscle spasm medication for up to 14 days after the accident.