A NEW publication from St John Ambulance, The Fast Guide to First- Aid, describes what steps to take in common emergencies such as burns, scalds, choking, drowning and head injuries. The easy-to-use, pocket-size guide costs pounds 4.90 and is available by post from Hascombe Enterprises, 17 Albemarle Street, London W1X 3HA, tel 071-409 7518.