These materials from the Centre for Clinical Interventions could give you a good start on using Behavioral Activation strategies.
An overview of behavioral activation (1 page)
The vicious cycle of depression (1 page): Describes the role of inactivity and withdrawal in maintaining depression.
Fun activities catalog (4 pages): A list of activities that might be fun and pleasurable.
Behavioral Strategies for Managing Depression (8 pages): A module from their workbook for depression, "Back from the Bluez."