Many essential oils are somewhat volatile and will quickly lose their scent if exposed to air, sunlight, or extreme temperature fluctuations.
1) Store your oils in dark glass bottles. Exposure to light can cause essential oils to oxidize rather quickly.
2) Make sure the caps are airtight. Exposure to air can cause oils to oxidize just as much as exposure to sunlight. Because of this, it's important to ensure that your bottles have an airtight seal.
3) Keep stored oils out of direct sunlight. Avoid storing your oil in any location that leaves oil in direct sunlight, including bathroom or bedroom shelves. Sunlight can cause oils to oxidize in just a few months.
4) Avoid heat sources. Most essential oils are flammable.
Keep the cap tightly closed on the bottle.
Keep/Store them a place where children and pets can not reach them!