No empty trips. A casual search suggests that this advice has its origins in the restaurant industry. Save time by consolidating. When you’re bringing the drinks for table two, if you’ve got room on the tray, get the calamari to table three. On your way back to the kitchen, grab the empty glasses from table four, those lushes.
I can’t remember when I first heard the phrase, but now I often hear it in my head. I come home, go upstairs with my bag full of sweaty gym clothes, toss them into the laundry basket. No empty trips whispers my brain. So I pack the now-empty gym bag for the next day and take it back downstairs. If I’m really on it, on my way back out I take out the trash, stopping at the car to throw the gym bag in the trunk. (Thus far I’ve managed to avoid putting the gym bag in the trash and the trash in the trunk, but sometimes it’s a struggle.)
I also think about it when I write. Say I have to get the protagonist from point A to point B. What can she be doing on the way that reveals more about who she is? “Put something into your character’s hands,” Franny Billingsley once advised. No empty trips.