All areas should have at least one help file, but what should be in them?
The following are some options you may wish to consider;
Unless your area is supposed to be hidden or difficult to find, then being reasonably clear with where it can be found will make it easier for players to get there, and encourage traffic. This could be quite specific, as in 'A recently discovered cellar in the Dragon's Bane Tavern in Midgaard has yielded a surprising discovery...'. Or it could be done by simply mentioning other areas adjacent or near your area, especially connecting areas, such as 'Deep within the Wildwood, somewhere to the south of Sir Michael's Stronghold a dark power has risen amongst the trees...'. Or you could get more vague, but still provide a general idea of where to look, as in 'Somewhere in the frozen northern wastes is a cave...'. Probably, even areas which are supposed to be reasonably obscure should have some hints or vague clues as to its location, as in 'Rumours of a new dragon of a ferocious nature have begun to surface all across Midgaardia. No-one seems to be sure where this dragon makes its lair (though many have theories). Jake the Thorn-Slayer has been gathering information, and it said would reward any who brought him some firm evidence...' In this example, we have a hint to maybe go and see Jake, and he may be able to clue players in - perhaps via mobprog or ticket. If you are especially kind, you may even mention the name of an individual mob in the area who could act as a portal point (generally at the front of the area), as in 'Sir Freddy guards the bridge which leads to the Citadel of Despair...'
If your area is strongly quest related, or has some overlying story which is generally meant to be uncovered by the players as they run/explore the area, then giving out some hints in the help file is a good place to start. The name of a mob which starts the quest could be a good starting point, the reward which you could get from the quest could help tempt people to search for the quest, some vague hints about the type of quest (slaying/exploration/riddles) could put people on the right track to find the start point themselves. Obviously, if you do have a quest - then part of the quest could be to find it.
A kind of hint, warnings relate to the dangers present in the area, as in 'Bring a boat.' Or 'Beware of corpse eating kzinti and their dietry concerns.' Other general warnings speaking of danger could be included in this category, such as 'A group of bold heroes - the Band of Fabulous Dudes - discovered this pyramid, and were the first to enter. Of the five of them, only Geraldolphus the Totally Amazing managed to escape alive to bring word of what happened back, and his ravings cannot be considered reliable.'
If your area has some interesting history or back story, then the help file is the perfect place to introduce it. If either of these are especially in depth, then the details may be found in edescs or objects, or various other places in the area, however the help file is a good place to present a general overview, or a surface impression. The true story of the area may even be different to that presented in the help file.
There is no rule saying that you can only have one help file connected with an area. At the end of your file, you may want to make reference to another help file which contains some specific information about a portion of your area - perhaps a particularly famous mob, perhaps details on a significant quest in the area you did not want to reference in the main help files, or perhaps some more OOC comments about the way the area works, the rules of the area, or the fact that CRs will be impossible in the area - the nature of which does not fit well with the IC style of the main help file.
Remember that if you put in a higher level help file with the same name, it should be before the more general file. It will also take precedence over the general file, so some duplication may be necessary. One way to avoid this to have the general help file called 'LAND OF DOOM', while the staff level help file be named 'LAND OF DOOM INFO'. If you feel that your area needs some extra explanation useful for Staff (Angels+) then this is a great place to store it. Details of problems with CRs, how to manually reset tricky quests, or even OOC comments from the builder on their motivations or ideas for building the area are possibilities, as would be comments about the previous area if the old area is being grandfathered and there is a need to comment on this.
Remember, the help file is an advertisement for your area. The more interesting it is, the more it will help your area stand out and bring in players.
Above all, help files for your area should be... helpful.