Sort get_users by custom field

By using this you can get your result in ascending order for sort_order custom field

$users = get_users(
   array(
   'meta_key'=> 'sort_order',
   'orderby' => 'meta_value_num',
   'order'   => 'ASC'
   )
);

foreach( $users as $user )
{
   echo '<h4>' . $user_info-> user_firstname . ' ' . $user_info-> user_lastname . '</h4>';
}