Hair cut, shave, wear a suit and tie, turn up bang on time, get out of the car and ring the door bell rather than sit there honking the horn, know the way to the destination, don't speed or drive like a lunatic, don't have some dodgy radio station on, take the beaded seat cover off the drivers seat and the christmas tree off the rear view mirror, don't tell some anecdote about who you had in the back of the cab, have plenty of change on you and refuse tips.
That ought to un-nerve all your passengers for the evening.