The next step is to design a "template" for the list items.  Our design will be fairly straightforward and simple.  Create a new MXML component based on the Canvas component.  Set the height to 22 and the width to 200.  Once you've added the component, switch to design mode.  Drag an Image component onto the stage.  In the Flex Properties panel, make sure you're in "Standard View" and select the layout tab.  On the left side you'll see 3 check boxes.  Select the center one.  On the right will pop up a text input with the current location of the image in relation to the vertical center of the stage.  Set this value to 0.  Along the top of the layout area are 3 more check boxes.  Select the left box.  In the corresponding text input at the bottom, change this value to 10. 
Next, open the "Common" tab (above the "Styles") and change the source field to "{data.image}" (less the ").
Drag out a "Label" component to the stage and place it somewhere to the right of the image component.  Open the Layout section of the Flex Properties window and select the center checkbox on the left and set the corresponding value to 0.  Select the left checkbox on top and set it's corresponding value to 34.  Also select the right check box and set it's corresponding value to 10.  This will extend the width of the label all the way out to 10 pixels from the right side of the components edge.
Open the Common tab and set the text property to "{data.label}" (less the ").  Your MXML code will look look like this:

<mx:Canvas xmlns:mx=http://www.adobe.com/2006/mxml" width="200" height="22">
 <mx:Image width="16" height="16" verticalCenter="0" left="10" source="{data.image}"/>
 <mx:Label text="{data.label}" verticalCenter="0" left="34" right="10"/>
</mx:Canvas>

 Now save your new component and close it's editor window.  In the next step, you'll incorporate it into your List component.