Step 1: Get out a half-gallon of fresh, raw, creamy milk from a source you trust-- grass fed and organic are not optional here.
Step 2: Gently heat the milk to between 101 and 118 degrees F. You don't want to go above 118 or else you will start killing the enzymes in the milk (thence kind of defeating the purpose of starting with raw milk, though of course it's still going to be better than most milk). The first time I did this I borrowed a friend's meat thermometer and stopped at precisely 110 degrees, noting how hot it felt on my pinky. Since then I guesstimate. It's about the right temp when you stick your finger in and it feels hot-- too hot to keep in for long but not so hot you scald yourself. The milk should not be boiling or frothing. I use a wooden spoon to stir it every so often. The milk heats up rather quickly.
Meanwhile, have your yogurt starter waiting in the bottom of the jars you'll use. Most sources recommend about 2 T of yogurt as a starter for a half gallon. I now guesstimate; a bit more or less doesn't seem to really make that much difference. You do want enough to jump start the fermentation, but not so much that it all turns to whey.
Optional Step 4- Thickening the Yogurt: I usually do this with half of the yogurt if it's too runny-- strain it through a coffee filter in a strainer over a glass bowl for a few hours. Keep the liquid (whey) and use it in smoothies, soaking grains, baking or as a probiotic supplement (it's tangy and not bad tasting). The yogurt remaining will be as thick and creamy as you want it to be. If you let it keep dripping then you'll end up with raw cream cheese (yum!!). I don't bother dripping the yogurt we use for smoothies since it gets slushed up anyway! :)
My favorite ways to enjoy yogurt are with just-fruit jam in it and a dusting of cinnamon, or with fresh or frozen berries, cinnamon, ginger and raw honey or Grade B maple syrup drizzled on it. Eowyn is quite a fan as well!