CBD oil should be stored in a safe place away from any heat, moisture, or direct sunlight.
For most people this would be a cabinet in their kitchen or bathroom, or a dry pantry.
Overall it's best to keep it somewhere that stays around or below 70 degrees Fahrenheit on average. This will keep the oil from degrading too quickly.
Some people in warmer and more humid climates tend to store their CBD oil in their refrigerator.
This is another solid option, although it may cause the oil to thicken over time.
If that ever happens, you can just run the outside of the bottle under a tap until it regains its original consistency.