Always use headlights when it's raining

I know this seems really trivial but it's so simple. When it's raining it's harder to see other cars unless they have their headlights on. So it's just common courtesy (which we could use lots more of) to turn on your headlights so other cars can see you. Plus in most states it's the law to have your headlights on if your windshield wipers are on!