Here are my personal guitar maintenance tips; note that the temperature and humidity values are not necessarily the ones recommended by experts, but more of what is within the controlled values in the room where i keep my guitars:
1. store guitars in hard cases in an upright position; do not place beside exterior walls
2. buy a digital hygrometer, mount it on a wall
3. place at least two silica gel packets inside cases (do not use those large dehumidifiers in canisters—they absorb water too fast and might do more harm than good when kept inside cases for long)
4. as much as possible, avoid using the guitar when the temperature is too hot and/or too humid (30.0 degrees Celsius, >67% humidity)
5. when temperature and humidity conditions are ideal, make it a habit to air out your guitars and cases (should be done at least once a week)
6. in our climate, air conditioning is generally good for guitars, but allow a few minutes for instruments to adjust to the cold temperature before taking them out of their cases; also watch out for the air becoming too dry (<30% humidity)