Why would you want to darn a sock when you can just throw away the socks with holes in them and buy new ones. Have you ever had a pair of socks that fit so well and felt so right, not to tight, stays up and very comfortable? This could be one of those times to darn. Perhaps you had a certain pair of socks that has been with you for a long time and feels like an old friend, this would be a good time to darn the socks and save an old friend. How about a "security" sock, the ones your child just loves. Sometimes it is the challenge, you just have to try your hand at darning. No matter what the reasons, you save bucks by repairing.
Darning socks is like trying to solve a puzzle. One must decide where to start and from there, the weaving begins, in and out until the patch is complete. Choose your wool that matches your sock in thickness and color. Find a round hard object to place inside the sock to hold the sock in place and maintain the hole in one position while you work on it. Start by turning the sock INSIDEOUT and work in good light.
For my examples I have used a different color of wool, so you can see the stitching.
Ball in sock

How to Thread the Needle
To thread the needle, fold the wool in half, about an inch from the end of the wool. Pinch the wool between your fingers, and press it against the eye of the needle. The wool will slip through the eyelet of the needle easily
How to Place the Stitches When Darning
When you start, do not make a knot at the end of the yarn, do about three stitches from the hole and leave about half an inch sticking out of the sock. From here on do an over the sock and then a under, on the other side of the hole.
Use double wool strand for work socks and single strand for dress socks. Each row will be the opposite of the preceding row. This will help blend the stitching to the sock.
On the far side of the hole, stitch a couple of stitches into the sock before coming the other way (back towards you). Always go a couple of stitches past the hole on both ends. When you run out of wool, just add new yarn into the needle and do two or three stitches into the sock and cut off leaving about a half inch sticking out of the sock (do not knot the end).
Completely cover the hole in one direction with wool, start the cross-stitches. It is under and over stitching until the hole is completed.
Turn the sock inside out again for a finished look.
How to Reinforce a Worn Sock
If you catch it early enough, before an actual hole develops, you can reinforce the area in question. Just start darning the area, using the worn, bare threads of the sock and weave in and out of them. You don't have to add the cross stitch, just go back and forth until the weak area is completely covered.
You can even stitch in reinforcement on a new sock, reinforce the area that will be the first spot to wear. This will extend the wear time for the sock. You can use a entirely different color to add some flair
Extra Tips on Darning Socks
Start with shorter pieces of wool, this lessens the wool from bunching into knots while drawing the wool through the strands.
Later you will learn how to let the wool "lay", off to the side to prevent this; you can then lengthen the wool as you master this technique.
At times, while darning, use the end of the needle to position the darned wool for consistency; this helps make for a professional looking job.
Way, way, back in elementary school, our teacher had everyone in the class, bring a darning needle, wool and a sock with a hole in it.
He was going to teach us how to darn a sock. In the first ten minutes, I had completed darning the hole in my sock and presented it to our teacher for inspection.
He took one look, took me aside, and wanted me to admit I had brought the completed darned sock from home and was pulling a "fast one".
I quickly came up with a solution to clear my name; let the teacher cut a new hole in the sock, and I would darn the hole and clear my name. Done!
I was quickly delegated to help other crying students who were having a difficult time.