If your yogurt comes out runny, try experimenting with the amount of starter, the type of starter, and the temperature if you can. I keep a database of yogurt so I can keep track of what works: culture medium, type and amount of starter, how long I let it culture, then the consistency, tartness and flavor of the result.
If you're making cow's milk yogurt, another option is to stir in some powdered milk before you scald the milk. Goat's milk always requires more starter than cow's.
Speed comes from what you put behind you. - Judi Ketteler