Using your favorite editor (vim), edit /etc/logrotate.conf.
At the end of logrotate.conf, add the full path to your log file followed by open and close curly brackets. There are many options you can add like the frequency to rotate "daily/weekly/monthly" and the number of rotations to keep "rotate 2/rotate 3". For a full list of options go to http://linuxcommand.org/man_pages/logrotate8.html. Each option gets added in between the curly brackets and on their own line.