OK, the easiest way to get cories to breed, is to have them in a species only tank.
First off, start out by feeding them nice meaty foods, bloodworm etc.
then after a three or four week conditioning, do a 50% water change during a rainstorm, and kick the temp down on your tank six or seven degrees.
preform 50% water changes daily for up to a week, or until you see signs of breeding.
No snails in the tank, or they will eat the eggs.
Basically they either will or won't breed. Some people can get them to breed consistantly, others have no luck at all ever.
hth.