The "mouth positions" are called
phonemes. They are the smallest unit of sound basically.
Here's a very useful image (you can find more on google images, which is where I found this):
One thing I've learned about lip syncing is that it's always best to exaggerate your morph targets a good deal. Then, you don't have to set the morph to 1, you can set it to something like .5 if needed. If you don't exaggerate though, and you want an exaggerated mouth pose and try to set the morph to something like 1.5 or 2, you have a much higher possibility of it becoming deformed. Just a little tip there.
Remember as well, the acting isn't entirely in the mouth. To give a character real expression, you really need eye and eyebrow expression.
Good luck.
