flowing and there is no risk of
igniting vapours.
.  
Brakes or chocks should be applied, but some places require brakes off when near fixed installations.

.  
Take out rescue and survival equipment so if the thing blows up you have something to hand.

The most important thing is daily checks, before flying. If you spill anything, either use a neutralising agent, move the aircraft or wait for it to evaporate before starting engines.
Fuel can burn you. High vapour concentrations irritate the eyes, nose, throat and lungs and may cause anasthaesia, headaches, dizziness and other central nervous system problems. Ingestion (as when siphoning while defuelling) may cause bronchopneumonia or similar nasties, including leukemia and death. If you get it on your clothes, ground yourself before removing any and rinse them in clean water. Fuel spills must be covered with dirt as quickly as possible.
Otherwise, everybody not involved should keep clear—at least 50m away, but for exceptions see later.

Passengers on Board
You should not normally refuel with passengers on board, especially when the engines are running, but in certain circumstances (i.e. casevac, bad weather, no transport, or on an oil rig) it may be permitted, if:
.  Passengers are warned that they must not produce ignition of any substance by any means (including switches). They must also remain seated, with belts/harnesses unfastened.
.  
"Fasten Seat Belt" signs are off, and NO SMOKING signs on, with interior lighting to identify emergency exits.

.  
A responsible person is at each main door which should be open and free from obstacles.

.  
Fuellers are notified if vapour is detected in the cabin.

.  
Ground activities do not create hazards; e.g. the fuel equipment should not stop people leaving in a hurry.

.  
ATC and the Fire Authority are informed.

.
Fire extinguishers are close by.

Note: Don’t re/defuel with Avgas or widecut fuel (e.g. Jet B or equivalent) or a mixture, when passengers are embarking, on board or disembarking.

Ditching
Ditching is a deliberate act, rather than an uncontrolled impact, although the terms are often used synonymously. A successful one depends on sea conditions, wind, type of aircraft and your skill, but it's the after effects, like survival and rescue that appear to cause the problems (88% of controlled ditchings happen without too many injuries, but over 50% of survivors die before help arrives).
Of course, the best way out of a ditching is not to get into one, but you can't always avoid flying over water. The next best thing is to prepare as much as possible beforehand, and make sure that the equipment you need is readily available, and not stuck in the baggage compartment where no-one can reach it. Have you really got enough fuel for the trip? Did you top up the oil or check the weather?