Is important! You need to make sure that the method you choose will keep your negatives flat and safe from damage. The cheapest way may not be the best course to take in the long run.
You can buy loose leaf pages in plastic or paper divided into six for 35mm film which will hold thirty-six frames cut into lengths of six. They have a white edge with ring binder holes that allow you to store the pages in albums/ folders or box folders. (I think the latter is the better solution from experience.) The white edge also means that you can write details on it like the method of development and/or a serial number, this will help you together with a contents list at the front of the album/folder to give you access to your negatives instantly.
The same type of leaves are used for medium format negatives 6x4.5 and 6x6. They are divided into four and the negatives are cut into lengths of four and three respectively.
It is important that the negatives are completely dry, before you load them into the storage leaf otherwise they will stick making it impossible to slide them in. If you still have trouble inserting them when they are dry you can snip off the corners of the leading frame of each strip.