This is just a snippet of text I got from here which I keep around and paste into my crontab on any new machine I set up. If I forget to do this I invariably end up googling it again... every time.

# CRONTAB REF
# from http://www.adminschoice.com/crontab-quick-reference
#
# *     *     *   *    *        command to be executed
# -     -     -   -    -
# |     |     |   |    |
# |     |     |   |    +----- day of week (0 - 6) (Sunday=0)
# |     |     |   +------- month (1 - 12)
# |     |     +--------- day of        month (1 - 31)
# |     +----------- hour (0 - 23)
# +------------- min (0 - 59)

01 01 * * * /usr/sbin/ntpdate -s 0.pool.ntp.org