I believe you have to talk to the drawer next to the computer while still awake. I think you have two options of using the shift to access a thumbnail version of effect menu, this mode also allows you to set a effect, I'll detail that later. The next option is just your favorite effect set to shift.
You can set your an effect for both options by going in the dream world, talking to the drawer next to the computer again while equipping an effect. Mix effects are valid options.