Lust goes from seeing sexual taunts , or getting aroused , best way is to either use seduction actions such as spanking your ass , or some enemies can try to get you that way too (the gobelins can use seduce) , or when someone sits on your face (just lay on the ground).
One of the easiest ways to increase lust for particular events is to get an enemy low on health, then grapple them and makeout. I've never had an enemy break out of a makeout so you can just spam whatever option adds to your lust, defeat them, then go do the encounter you needed high lust.
You can use the Anal Beads from the Strange Merchant, equip and unequip them to increase the Lust, in may case i get +3-4% Lust each time when i "unequip" them.
