DO NOT work outside the hand rails on the boatdeck, casing top or whaleback. DO NOT leave liver boiler lids open. DO NOT fail to keep a weather eye open for approaching seas or ignore warnings regarding water coming on board - prompt action saves lives. DO NOT step on the trawl - this is likely to run outboard. DO NOT fail to carry out the strict drill on all occasions when working the gear.
Splices are a particular danger.
DO NOT negotiate ladders in an unseamanlike manner. Always face the ladder and use the hand holds and rails provided. DO NOT stand under hatches or suspended loads. DO NOT operate any of the winch motions until you are sure everyone is clear. Modern winches are powerful, non-yielding and silent.