Simultaneous Edit & Play
One really useful thing you can do is to be writing your markdown and at the same time see the output being rendered in Play mode, the way a student will see it.
The simplest way to handle things is to switch Layout mode to Split View mode by selecting the 2nd from left button in the header bar.
You should now have something like the screenshot below. As you enter your Markdown content in the Guide editor, you will see the Preview window updated simultaneously.
You can also manage your own custom panel configuration at any time as explained here.