Help and task context

Begin help by outlining the purpose of the particular help window

Provide directions for the completion of a goal

Give the relationship between each action/task in the context of the goal

Discuss how the application treats a particular domain concept

Where a specific syntax is required, specify that syntax, with examples

Help often used in one of two ways:

Context-sensitive help
Browse-to-learn

Keep writing simple, concrete and oriented toward user group

Finally, do not deliver an error message if it really is not necessary...