There are four key factors that will affect the quality as well as the storage-life of your longer-term food storage. Those four factors are temperature, moisture, light and pests.
Store products at a temperature of 75°F/24°C or lower whenever possible. If storage temperatures are higher, rotate products as needed to maintain quality. (Provident Living)
Common storage areas such as attics and garages are likely going be very warm and will reduce the storage life of your food. A basement or the main floor of your home would provide cooler temperatures. Also, interior rooms are less affected by the temperature swings outside.
Keep storage areas dry. It is best to keep containers off of the floor to allow for air circulation. (Provident Living)
Setting products on pallets or even just a few untreated 2x4s gets items off the floor. Moisture is the main reason that buckets are not recommended for storage unless you live in a very dry climate. #10 cans and/or Mylar bags do a better job of keeping moisture out of your food storage.
Protect cooking oil and products stored in PETE bottles from light. (Provident Living)
Closets, pantries and windowless rooms would be great to keep products out of the light. This is more of an issue for foods that are stored in semi-opaque or transparent containers (like PETE bottles, canning bottles, or semi-opaque buckets).
Insects and rodents:
Protect products stored in foil pouches and PETE bottles from rodent and insect damage. (Provident Living)
Pests are persistent and can chew through almost any container. Mylar pouches are particularly susceptible to rodent infiltration. Plastic buckets or bins are also quickly penetrated. #10 cans or steel drums provide the best protection, but even they can be compromised.
Make sure that you purchase and store clean, pest-free products. Oxygen-absorbers can help eliminate any insects that arrive with your storage products (but are usually only effective in #10 cans, Mylar bags or PETE containers). Clean your storage area regularly and watch for signs of pests. Over time a fine food-dust can settle in your storage area and provide perfect conditions for weevils or other insects to spread. Wipe down all areas, including the floor to discourage insects.
[We had a major weevil infiltration in my childhood home storage room. Though my mother kept the area clean, the weevils had spread through this fine dust throughout the entire dedicated storage room. She ended up throwing out her custom rolling shelves because they couldn't be cleaned out. I purchased a wire-style shelf for my own storage to help prevent any similar problems.]
By paying attention to these four storage conditions, you can lengthen the storage-life of both your three-month supply as well as your longer-term storage.