Cacher is the code snippet organizer for pro developers

<?php
function myplugin_insert_customs($pid){

    $customs = array(
    'post_id' => $pid,
    'meta_key' => 'Your meta key',
    'meta_value' => 'Your meta value',
    );

    add_post_meta($customs);

}

add_action('save_post', 'myplugin_insert_customs', 99);