These rules are defined at a local level and are not 'officially' part of the 34 rules of golf. The rules appear in the appendix which gives local courses, clubs and committees the power to let their members take relief from substandard conditions and repair works on a course.
Winter rules differ from course to course and under tournament conditions a player must ask or be instructed as to what interpretation each course uses. Under no circumstance should a player, under tournament conditions for the purpose of handicap, assume his own version of the rules without proper instruction from the tournament's organisers.
If you are submitting a card for handicap purposes you must state that your round was played under 'winter rules'. However if you are simply having a friendly round these rules can be decided by all participating parties with regard to scoring.
Winter rules, or 'preferred lies', usually focus on gaining relief only on the fairway. When a course is very wet or waterlogged then shots that would usually produce an ideal lie on the fairway will often plug producing a disadvantageous or unhittable lie.
Winter rules allow a player, hitting from the fairway, to mark, clean and place his ball on a better lie no closer to the hole. The distance from the mark can vary from one club length to one score card length depending on the course, so you must check in advance.
If a ball comes to rest anywhere outside of the fairway then a player must play it as it lies. This includes the rough, putting surfaces, tees boxes and hazards including bunkers. Note that if you are on the fringe of the green you can mark and replace your ball as instructed but you can't place it on the putting surface even if you place it further from the hole.
Preferred Lies may also come into play if there are repairs or 'drought damage' to a course. Repair works will generally be sign-posted or roped off signalling that you can get relief as if it was a manmade hazard. In this instance you may pick up the ball and place it behind the designated hazard area, no closer to the hole.
During winter conditions these rules are intended to keep scoring consistent and not to penalise a golfer for circumstances outside of their control. As always you must be careful to adhere to the local committee rules and never take it upon yourself to enforce winter rules under tournament conditions. That is defined as cheating and you would be disqualified. However playing legally to winter rules should give players limited relief and allow them to play to their potential no matter what the conditions.
Should you wish, you may also choose to ignore the winter rules and play your ball as it lies.
