How can I add few css or js file into my plugin

if( ! function_exists( 'style' )){

    function style() {
        wp_enqueue_script('jquery');
        wp_enqueue_style ( 'my-admin-theme', plugins_url ( 'style.css', __FILE__ ) );
        //wp_enqueue_script ( 'jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js', array (), '1.0.0', true ); // already included jQuery
        wp_enqueue_script ( 'uploadfile', 'http://hayageek.github.io/jQuery-Upload-File/jquery.uploadfile.min.js', array (), '1.0.0', true );
    }

        add_action( 'wp_enqueue_scripts', 'style' );
        add_action ( 'admin_enqueue_scripts', 'style' );
        add_action ( 'login_enqueue_scripts', 'style' );

}else{
    echo 'Function already exists'; 
}

Try next code, but your code work. No need to include jQuery, because by default WP use it.