I always use one second per knot per minute in still air.
Some procedures have 30 seconds outbound before commencing the pt - lets say you have a 30 kt tailwind. As its only 30 seconds in still air (ie half a minute) you take half the wind as correction - in this case half of thirty = 15 - apply this to the 30 seconds still air to get 15 secs outbound before comencing the pt.
Remember though that the really important thing is to get the correction in the correct sense and that an examiner just wants to see that you make a sensible wind correction so keep it simple!