EditPageTrick

EditPageTrick is an extension that allows for the creation of "editing tips", which will show up above the edit window, requiring only a simple template be created to make this work.

This can be useful for giving advice to new and experienced editors alike about specific editing expectations, how to use specific markup, or just any random message you deem appropriate while editing.

You can also use the various site notice headers in the MediaWiki namespace to do the same thing, so this is just an alternative method.