using wp_enqueue_scripts and admin_enqueue_scripts

wp-script-calls.php

// front end
function custom_front_scripts() {
	wp_enqueue_style( 'front-css', plugins_url('/lib/css/front-css.css', __FILE__), array(), null, 'all' );
	wp_enqueue_script( 'front-init', plugins_url('/lib/js/front.init.js', __FILE__) , array('jquery'), null, true );
}

add_action('wp_enqueue_scripts', 'custom_front_scripts' );

// back end
function custom_admin_scripts() {
	wp_enqueue_style( 'admin-css', plugins_url('/lib/css/admin.css', __FILE__), array(), null, 'all' );
	wp_enqueue_script( 'admin-init', plugins_url('/lib/js/admin.init.js', __FILE__) , array('jquery'), null, true );
}
add_action('admin_enqueue_scripts',	'custom_admin_scripts' );