wp_enqueue_script not working?

You could use only one function to do all because it’s the same hook wp_enqueue_scripts:

add_action( 'wp_enqueue_scripts', 'my_scripts_method' );
function my_scripts_method() {
   //global $wp_styles; //here no use unless you have to use it in a conditional stylesheet for example
   wp_enqueue_style( 'twentytwelve-style', get_stylesheet_uri() );
   wp_enqueue_script('custom-script', get_stylesheet_directory_uri() . '/js/trans.js',array( 'jquery'), null, false );
   );
}

It’s no use modifying the header.php, actually it’s better to handle scripts and stylesheets in functions.php (or in a plugin) than hard coding templates. The recommanded way is to enqueue your stylesheets and scripts because you get a better control (dependencies, load, etc).