Following a truck accident, if you are able, call 911 or make sure someone else does. This will ensure that the police and an ambulance arrive at the scene. The police will gather information to put into their report.
Obtain witness contact information and take photos at the scene if you are able. Never admit fault, even if you think you might be partially responsible.
Once you are home, contact your own insurance company to notify them of the accident, then contact an attorney. Jot down everything you can remember about the accident.