Dieffenbachias like dappled sun but not complete shade. Give it bright indirect sun and your dieffenbachia will be happy. They like to be drenched with water but then they like to be left alone to dry. In very warm months they require a bit more water and, of course, during the winter slow down on watering.1
Try to plant in a location that enjoys dappled sun and remember to water moderately.Dumb cane, dieffenbachia maculata