How to Set Post Thumbnail Size for Genesis's Child Themes

This is rather easy. In your functions.php file, add this one line of code.
[php]// Add Post Thumbnail Support
set_post_thumbnail_size(300, 165, TRUE);[/php]

For more information on set_post_thumbnail_size, see the WordPress Codex, but generally speaking here is the usage:
[php]<?php set_post_thumbnail_size( $width, $height, $crop ); ?> [/php]