Simplest way is roughly equal parts water and feed. Mix in a large jar or food safe container. Don't cover/loosely cover, it needs to breathe. By 24 hours it's ready to start feeding, and I feed it once a day until I run out (I usually make about 3-4 days worth), then add more water and feed to container and start it up again.
My goal is to achieve a very thick, oatmeal like product with little/no extra water.