1) Make sure your passenger confirms an address before driving off. A nice American family asked me to take them to Reubens from Haymarket last week. No worries: we sped to Baker Street and I proudly dropped them right outside the door of the esteemed kosher restaurant. When they asked where the hotel was, I realised in horror they wanted Rubens Hotel near Buckingham Palace. That cost me! They were fine about it though.
2) If you use an automatic car wash, make sure you close the rear windows first. It’ll save you the job of wiping down the interior and partition screen.
3) One from the past: always remember that your cab runs on diesel, not petrol. This is a very expensive and embarrassing mistake.