the $fields array is very important for accessing field content when doing custom theming. Unfortunately field names are not well documented, nor are they intuitive. For example, the field name for a node:link field is view_node. In order to track down names of my fields I usually use print_r … the trick here is that you must look for ‘stdClass Object’, almost always the index giving these objects as values are the names of the fields used within the $fields array.
[field_image_fid] => stdClass Object ( [content] =>
can be accessed in your tpl.php by: