Having clean headlights and taillights helps makes it easier for you to see other vehicles and makes your car more visible to others. It's a good idea to clean your headlights and taillights whenever you get gas using the squeegee provided by most stations. You may also want to carry a spray bottle filled with windshield washer fluid and some rags or paper towels with you so that you can easily clean your headlights and windows even if there aren't any garages around.
If your headlights have condensation in them you can try driving with your headlights on during the day to try and evaporate the water. If this does not work you may need to remove the headlight housings from the car to inspect them for cracks and to allow them to dry out. You can speed up the drying process and clean the inside of the headlights by adding some rubbing alcohol to the housings, swirling it around, and then draining it out. Any cracks in the headlight can allow water to enter, you can try repairing them with glue or sealant. Some headlights have vents (small holes or tubes that allow water to escape) and condensation can build up when these get blocked, so ensure that any vents are clean.