Suggest that new users have "Show me both editor tabs", by default. As they are new, would appear a floating bar with the message, for the first edits:

<div style="text-align:right;"><big /> [ X ]</div>
<center><span style="color:blue;">Change</span> editing mode (your can easily come back, clicking in <span style="color:blue;">return</span>).<br> 
You can close this bar (you can see it again in your go on editions) or <span style="color:blue;">turn off</span> forever.</center>
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*How it works: if you are in your first edition and click in "Edit source" (Source / Code Editor), you can change to the visual editor, clicking in this floating bar in the word "Change"). Then, you can come back to the source editor clicking in the "return" button.
*And viceversa: if you are in your first edition and click in "Edit" (VisualEditor), you can change to the code editor, clicking in this floating bar in the word "Change"). Then, you can come back to the visual editor clicking in the "return" button.
*You can close this bar, clicking in the cross (X).
*Your can turn on this bar forever clicking in the "turn-off".
*From a certain number of edition times (i.e. 10 or whatever number elected by default) the bar is automatically turned-off forver.