How do I determine how much drainage I need in my pottery?

The average houseplant or annual pot outside needs good drainage. The soil in the pot should feel moist after watering, but not have pooled water on the soil surface. There are some special cases- carnivorous plants for instance, like to be soaking wet, and want little to no drainage at all. Cacti on the other hand want very little water and should have very fast draining soil.