These are the three things your oils hate.
So keep them in a cool, dark place. If you can, put them inside your ref but make sure to put the bottles in sealed containers like the microwaveable ones, so that their aroma, if ever it leaks, would not mix with other contents of your ref.
Oxygen – always keep your bottle closed. If you have big bottles that are halfway full, best to transfer them to small ones so that there is little space inside the bottle for oxygen molecules to occupy.