Chavant has a couple DVD's out on sculpting for mold making. They may be available where you got the clay. Are you wanting to make a regular latex puppet or a foam latex one? They are two different processes. Foam latex is injected into a mold where as just regular latex can be slushed or pored into a mold then closed up. Foam latex is a bit more involved but is what most stop motion puppet makers use to make their puppets. Below is the second video in a series of that process.
http://youtu.be/_W7gCMNr5k0Even if you are not making a stop motion puppet with an armature it should give you some decent basic tips. One of the most basic of tips in any of the processes would be that you want to sculpt the mouth in the open position which actually is the same rule for making puppet out of sheet foam or carving them out of block foam.