I've basically acquired my information via Google and here over the years so I don't have any one place.
You can start by running:
/usr/local/cpanel/3rdparty/mysqltuner/mysqltuner.pl
from your root shell and see what recommendations it has. Then you can google those settings for more information. Settings and syntax are dependent on your version of MySQL, and the current specs for your server (such as available memory), so don't just copy paste everything you find people discussing. Be sure to read up on the setting in the mysql.com manual and other places that discuss it. Note that if something should go awry, you can also remove the setting and restart MySQL again from WHM.