Kali is the Goddess of Death, which you will encounter pretty early in the game. She is represented by a gigantic statue with a bloody altar beneath her. To get this achievement, you will need 16 Favor with Kali, which is gained by sacrificing stunned or dead bodies by placing them on the altar. You can see a list of points here: http://spelunky.wikia.com/wiki/Altar
I suggest going for this in the Jungle. Try to get sacrifice two stunned Cavemen for 4 points (be careful that they don't un-stun in your arms), then sacrifice the Damsel afterwards.
Another easy tactic to get it is to simply sacrifice two Damsels. This leaves you with less health than you would have with the tactic above, but that might not pose a problem if you are solely going for this achievement, in which case sacrificing two Damsels at the first two Altars you see would be the best option.