The more I learn about conservation and frugality, the more I re-discover what my grandparents knew. In this case it's darning. I vastly prefer the warmth and comfort of wool socks, glove liners and sweaters to cotton and most synthetics. Those same wool garments (especially socks) consistently wear out in the same places. Instead of throwing out mostly-good wool socks I've started darning (mending) them and extending their useful life.
Start your darning with a pair of socks (or other knit woolen), wool yarn of a similar gauge (thickness), a needle fat enough to thread the yarn, and a darning egg or ball. All of these items can be found at your local fabric, craft or knitting store. Place the ball/darning egg in your sock at the toe or heel to support your sewing. Thread your yarn (a contrasting color will help you see your work) and sew through the wool knit creating a 'box' around the hole. Next, sew across the sock, from one side of the 'box' to the other. Lastly, sew from top to bottom of the 'box' creating a woven patch which reinforces the wool knit. If my explanation wasn't clear, here is an illustrated guide to darning.
Darning is a ridiculously simple and inexpensive way to extend the life of socks, sweaters and other knit wool clothes. I only just re-discovered darning because I saw one of my wife's friends skillfully darn a pair of ragg wool socks. Once I saw how darning was done, I had to try it for myself. I often darn a pair of socks in the evening while watching TV or listening to the radio.
Now that I'm darning my woolens, I should probably stuff a few pieces of cedar into the sock drawer too.
Knitty.com - Repairing Knitwear