The most important thing to know when using Exif/metadata in investigations is that they can be faked in a minute using online services:
http://thexifer.net
http://imgonline.com.ua/exif-editor.php
http://sejda.com/edit-pdf-metadata
Never trust exif data without further verification.
One possible sign of metadata forgery is that the names of files and folders are too expressive. Ordinary person's directories are called "new folder (56)" and "my docs".
If the exif's file path has strange names (such as "eagle flight"), this is a reason for additional checks.
