Repair sticky windows which don't open
At night, turn on porch light and outdoor lighting
Clean all switchplates
Clean all windows, inside and out
Clean existing shutters, blinds, drapes and ceiling fans
Clean skylight for leaves and other debris
Increase the wattage of bulbs to maximum possible wattage
Install dimming switches in common rooms such as dining rooms and living rooms to allow you to create lighting for different occasions
Install new window treatments if those you have are damaged or dated
Keep curtains open and use natural light as much as possible
Make sure all outdoor lighting works
Prune outside trees to allow natural light inside
Turn on enough lights so home is well lit during showing
Wipe all light fixtures with a rag and cleaning solution