You need an airtight container that's made to store food. A 5 gallon bucket is a good option. My mom used to store it in gallon ziplock bags within the bucket which is brilliant so you don't expose all of it when you open the top and it's a lot easier to manager. Then you add oxygen absorbers (which are pretty cheap). Then store the bucket in a place that's cool - no hotter than 70 degrees. The flour will last for years!