Most publications use an editorial calendar to plan out their stories and features.
An editorial calendar is published at the end of each year for the next year. It is developed by the editorial staff of magazines and details the planned coverage for the following year. Some newspapers and Internet sites are developing editorial calendars these days too.
I just want to note that this post concentrates on magazine publishers. There is tremendous opportunity to apply this strategy to local and national newspapers. The timetable to do this is much more immediate than the 3-5 months indicated for magazines though.