You can create a popup message that appears when a user first opens the ME editor. This popup will give the user any relevant information/instructions they may need when using the editor.

Using editable content blocks and assigning one to the MegaEdit product you want to display the message on. 

Navigate to Editable Content in Admin and search for Infigo Editor Instruction Panel (Admin > Content Management > Editable Content > Infigo Editor Instruction Panel.)

In there, you can edit what you want the pop-up message to say.

and then assign it to a product using the instructions tab in the MegaEdit Config.

(Or you could create your own content block. Navigate to Editable Content in Admin and under the custom tab section add a new content block. You could call it "MegaEdit instruction panel 1" for example. You can adjust the content as you require.  Then simply assign that to any product under the MegaEdit product section for instructions.
 
Alternatively, dou could also set up a non-clickable text box within the editor that is placed off the canvas. Something like this:

You would need to add a new text field, adjust the field settings to make it unable to be selected by the customer, and save it as product default.