Here are the steps:
1) Heat a gallon of milk* in a pot to the point that it starts to have little bubbles around side and forms a skin on top.
2) Discard the milk skin and pour the milk into a cold crockpot liner (the ceramic part).
3) Let the milk cool down for a while. It should be warm but not burn your finger.
4) Mix in about a cup of yogurt starter.
5) Put the glass lid on the crockpot liner.
6) Put the crockpot liner, milk, and lid (all together, of course) in the oven.
7) Turn on the oven light (must be an incandescent bulb because you need its heat).
8) Let the yogurt incubate overnight in the warm oven. (DON'T TURN ON THE OVEN. Just the oven light.)
Voilà!. Yummy homemade yogurt for minimal cost. It's going to be runnier than the stuff from the store because you don't add pectin, but who needs solid yogurt when you're going to be mixing it with muesli or granola or using it in recipes like naan?
By the way, I make no guarantee that this will work in everyone else's kitchen. If your oven light isn't warm enough, if your crockpot liner is thicker than mine, etc., you might just end up with gross milk in the morning.
* I like to use whole milk. It makes thicker and tastier yogurt.