In a short story you have between 800 and 3,000 words, on average, in which to tell your tale. You can't afford to introduce a cast of epic proportions. They simply won't fit in.

So what must you do, what principles must you abide by to get the balance right? Let's look at one or two examples.

Principle 1 - As often as possible cut them out.

Your main character is John and you write: 'John opened the door. It was Reg Bigley, the postman, with a parcel.'

Giving the postman a name makes him a 'Character' and, as a result, in the minds of your readers he has assumed a visual reality. Your readers see the name 'Reg Bigley' and immediately see in their mind's eye the kind of person that name means to them. It will differ from reader to reader of course, but giving a character a name will have that effect.

If you write: 'John opened the door. It was the postman with a parcel' then we just have a nebulous 'postman' with no connotations for building a persona out of.

In this scenario I am assuming the parcel is the significant factor, and if you can get away without the actual appearance of the postman, so much the better.

So you could write: 'John was in a quandary. The postman had brought the parcel that morning, but the contents were decidedly not what he was expecting'

Lesson: Don't give minor 'walk on' characters names, and if you can do without them altogether, do so.

Principle 2 - Do they have a plot turning role?

Let's update our previous scenario. This time you write:

'John opened the door. It was Reg Bigley, the postman, delivering a parcel.

"Hello Reg, what is it this time?"

"Another for your DVD collection I reckon, John."

"You could be right. Got time for a cup of tea?"

"Ta very much." '

Now you are giving Reg more than a 'walk on' role, plus we have the beginnings of a personality. This poses some questions. Does Reg play a serious part in the actual plot? Does he have some knowledge about the parcel that will have a bearing on the plot? Is he going to appear more than once? How many cups of tea will he drink?

If the parcel is significant, as we have assumed, but Reg only appears once and is then forgotten, keep him simply as the postman with no name. If Reg will contribute to the plot in some way, or if his conversation with John will bring something pertinent to light, then giving him a name and a personality will work so long as you don't overdo it.

If you are bringing Reg back later in the story with an important contribution to make, then OK. Just refrain from giving him a wife, four kids and a guinea pig.

Lesson: A character must add significantly to the plot to make them worth the precious word count they're going to take up in the story. If they don't, keep him or her low key and anonymous at most.

Keeping lesser characters to a minimum will result in a sharper, more focused story for your readers to enjoy.