The best time to buy bananas is when they go on sale. Sometimes, if you're lucky, some of the bunches are already turning brown.
Purchase bananas and set on the counter or kitchen table until they are a lovely shade of brown.
When ready, peel the bananas. If you have a large amount of bananas to freeze, fill a bowl with cold water and a tablespoon of lemon juice. Dip each peeled banana in the bowl of water, place them in a freezer bag, and freeze.
If you just have one or two bananas to freeze and are saving up to make a loaf of banana bread, just peel the bananas, bag, and freeze. The bananas may brown slightly with this method, but it does not affect the taste.