Are there any pointers, or standard practise for this? 

 

Perhaps, possibly, everyone has their own style and there are no hard and fast rules for creating help pages. 

 

I've done a couple projects where the help is stored in a table, with a record for each layout (this can be extended to tabs and fields). Clicking the "help" button runs a script that pops up a new window, goes to the help layout, and searches for the layout name, which is stored in a field. If it finds a match, the script exits, and the user is looking at the help text. If no match, it creates a new record with default wording, and a user with appropriate access privileges can begin editing.

so it works like a wiki too in a way? Sounds like a really good idea.  I need to get into the habit of implementing my ideas in fm tables, that is my ideas other than the core db ones.

Calling it a wiki is stretching it quite a bit. A wiki is not a bad approach, though, and I've seen some solutions that feature documentation in an actual wiki, displayed in a FileMaker web viewer.

using a "Help" source outside the file itself is always a good choice when you have to update the help.

a wiki isn't the worst idea, same to pdfs stored remotely… or simple "Insert from URL" pointing to a text file stored on your server.