Here is some popular command when you set a cronjob up for Magento by SSH.

1. Setup cronjob run every 5 minutes:

*/5 * * * * wget -O /dev/null -q http://www.example.com/cron.php > /dev/null    

or

*/5 * * * * /bin/sh /[magento_path]/cron.sh

2. Setup running reindex data every 60 minutes:

*/60 * * * * php /directory_to_magento/shell/indexer.php reindexall