There isn't too much consistency, unfortunately. Using an example most people would be familiar with, check out
one of the giants in Kael. (You may have to click "login as guest", then try the link again.)
Killing one will give you +10 faction for Coldain and Claws of Veeshan, and -30 to all of the Giant factions. That's usually the scale used, if not the exact values. 10 and 30 are pretty big hits. I'd drop a zero off each if we were worried about using a more Live-like faction. However, having negative hits weighted 3:1 over positive hits seems to be pretty accurate.
Hope this helps.