Buy your ticket or top up oyster card in advance... Staff here are the worst! When there is problem, nobody is here to help & trains are often late! Grrrrr!
Watch out for the one armed "homeless" man usually at the last carriage on the London train he walks thru all carriages shouting and begging each passenger for money - always there about 111am-2pm
Waiting room although very warm in the winter is generally frequented by people lacking social skills between 7am and 8am. Try to avoid unless you have nerves of steel (or a good solicitor).