State those assumptions in the preface and stick to them.

Manuals change hands plus the business manager may want it but some someone else may be handed the manual to manage the site.

Stop; go out, do whatever.

Now, play back that video extra slow, pausing every time you do something, and write that thing down. Add screenshots of every key stage and the layout of every menu. Every time you give something a name, include a picture of it; no discussing the 'customer administration menu' without a picture nearby.

Provide a section entitled 'how to' which lists all the key tasks with references.

How to:
- Delete a client from the mailing list (4)
- Ask henry0 for his home phone number (6)
- Rewire a plug (9,10)

In the index, do the same thing but almost backwards:
- Clients: (4-12)
. - Deleting (4)
. - Exporting (11)
- Henry0 (13, p.14)
. - Home phone (13)
. - Bank details (14)

Finally, get someone capable of the job, and preferably someone who's not familiar with your system, to proof read it.

If I wrote down how I thought it should be done, I missed out some real obvious things, such as scroll down the screen for the answer. I found it much easier to shadow current members of staff to see how they operated the equipment and systems.

So, what I was indicating is to get someone less familiar to press the keys and operate the system, and as vvv said, write it all down.

Pictures, screen shots and sample forms help, too.

Once done, run through it again to check it.

It really is worth the effort in the end.