We learned in testing that a 50-50 mix of whole-wheat and all-purpose flours works much faster than all-purpose flour alone, because the whole-wheat flour provides more nutrition for the budding organisms.
Using filtered or bottled water is also important, because chlorine in tap water can kill the starter.
The first stage is to make sure the microorganisms are alive and consuming nutrients. At this point, the loose, batter-like mixture smells like sour milk, but it’s a positive sign that the starter is established.
Then feeding begins. Many recipes call for feeding every 12 hours, but every 24 hours is totally sufficient. After about two weeks of feedings, your starter will be pleasantly aromatic and ready for baking.