Know Your Humidity
For proper guitar maintenance, control the temperature and humidity whenever possible.
Purchase a hygrometer/thermometer and keep it in your case. If you afford it, purchase two. Put the second one in the room where you typically store your guitar.
Keep the temperature and humidity at recommended levels. Check your product manual. If you have no product literature, the most common recommendations I've seen are for 68-77 degrees Fahrenheit and 45-55% relative humidity.
If the area is too dry, use a humidifier to raise the moisture level in the room. You can use a guitar humidifier, such as the one made by Dampit, or a room or house humidifier.
If you use a Dampit, or other small humidifier, make sure you wipe any excess water off before inserting it into your instrument's sound hole, or the case. If you use a room or house humidifier, never allow the moist air to blow directly on your guitar. If the area is too wet, use a dehumidifier to lower the moisture level. Never allow a heating or cooling vent to blow directly on your guitar!
To minimize the affect of changes in temperature and humidity levels, keep your guitar in its case. Also, never store it in the direct path of a vent or against an outside wall where temperature and humidity can be significantly different from the rest of the room and can change rapidly.