Stop, drop, and roll, says the National Fire Protection Association. From NFPA Standard 45: Standard on Fire Protection for Laboratories using Chemicals, 2015 Edition:
A.6.5.3.2 Laboratory personnel should be thoroughly indoctrinated in procedures to follow in cases of clothing fires. The most important instruction, one that should be stressed until it becomes second nature to all personnel, is to immediately drop to the floor and roll. All personnel should recognize that, in case of ignition of another person's clothing, they should immediately knock that person to the floor and roll that person around to smother the flames. Too often a person will panic and run if clothing ignites, resulting in more severe, often fatal, burn injuries.
Fire-retardant or flame-resistant clothing is one option available to help reduce the occurrence of clothing fires. Refer to NFPA 1975 for performance requirements and test methods for fire-resistant clothing.
It should be emphasized that use of safety showers, fire blankets, or fire extinguishers are of secondary importance. These items should be used only when immediately at hand. It should be recognized that rolling on the floor not only smothers the fire but also helps to keep flames out of the victim's face, reducing inhalation of smoke.