Interesting article from WritersUA on Design Checklists for Online Help, where 'online help' is defined as "'brief task-oriented modules of information' that support the user in accomplishing their tasks."

Among other things:

• Make the information task-oriented and highly structured, because the purpose of online help is to get the user back on task as fast as possible
• Separate information into distinct information types and include only one information type in each online help topic
• Follow minimalist principles in designing online help topics. Many online help designers misconstrue minimalism to simply mean brevity; however, minimalist design hinges on being able to make good decisions on what to do, say, or show, and on what not to include
• Keep the length of topics short, perhaps to no more than two screens long