My favourite is the full and free check of all flight controls before each flight.
I know that this check is instilled into the minds of all new pilots from day one / flight one, however, I am stunned at the amount of times I have been a passenger in an aircraft where this basic check is expected, but not carried out ( in some aircraft, this check cannot be carried out due to hydraulics )
I have had the unfortunate experience of being on scene of an accident where 17 souls were lost on a fixed wing due to a control restriction.
How much effort does this check take?