Instruments like to be in the same environment as we do: Not too cold, not too hot, and not too damp. Store your guitars in an area with an average humidity of 45 – 50%, and a temperature of approximately 70 – 75 degrees F. If the ambient conditions are very damp, then use a dehumidifier. Conversely, if the ambient conditions are dry, then use a guitar humidifier.
The best method for storing acoustic guitars especially, but electrics too, is in their cases but of course, we all like to view and appreciate our beautiful instruments and keeping them out of their cases and ready to play definitely encourages us to use them more, but be careful of the sun and dust when storing outside of their cases. Definitely keep them away from windows where it can be extra hot, cold, or drafty. If they’re out of their cases and near a window, the sun can wreak havoc on the finish and colors. And when storing them for a prolonged length of time, keep tension on the strings to keep the neck under the same and constant tension.
Hope this helps!