Lights on when you're out or away and doors locked when you're in on your own.
I always leave upstairs landing lights and/or bedroom lights on if we're away. No one knows they're on during the day but give the impression there's someone upstairs at night. And bulbs are pennies to run, why bother with a timer? There's also an outside light at the back that's always on at night. In fact our house is rarely in darkness at all. A habit I got into when we had kids so if any of them get up they're not stumbling around in the dark. One of the neighbours is frequently away and their house might as well have a big "Burgle Me!" sign over it.
Locked doors because in our last house we had chancers opening the back door even when I was sat in the living room.