sorry I can't give you proportions. tomorrow I can ask my mom, if you like. It's best if you have a gas range with a pilot light, IMO. basically, you boil some milk, let it cool. add a tablespoon or 2 of existing yogurt and mix it up and leave it in the oven overnight. I don't have a gas range, so my mom told me to heat it to 200 turn it off and put the cooled boiled milk/yogurt mix in there overnight. I've heard of people keeping it near their radiators, or anything else that emits a low but steady supply of heat.
If you need proportions, I'll ask tomorrow. my guess is though, that there's a lot of latitude in them.