Once a sock knitter has completed that first sock and realized that in fact they're not only not scary, but actually pretty fun, the biggest fear becomes, "What if I get a hole in them?" Therefore, let's talk about hole prevention and repair, and we'll cover a little general sock maintenance while we're at it.
First, there are things you can do in the knitting process that will make your socks less prone to holes. A sock knit at a tighter gauge wears better than a looser one, so knitting at a minimum of 8 stitches per inch is a great idea, and knitting at 10 st/in is even better. It's also possible to add reinforcing thread/yarn in the knitting process, particularly at the heels and toes which tend to be high-wear spots. There are specialty sock reinforcement yarns sold for this purpose, and a few brands of sock yarn come with a matching spool tucked right into the ball. Many people also like Woolly Nylon, which is a thread sold for use in sergers (a specialized type of sewing machine); this yarn is 100% nylon, with a fair amount of stretch to it that allows it to move well with the sock yarn, and a soft texture, which means it tends to feel fine on the feet, and it comes in a large number of colors so a good choice should be easy to find. With either sock reinforcement yarn or Woolly Nylon, the reinforcement can be knit right along with the sock yarn, usually without a change in gauge. It's also possible to just double-strand the yarn you're already using for the heels and toes, but you may need to go down a few needle sizes to maintain your gauge. You can also use a reinforcing stitch pattern, like the heel stitch or eye-of-partridge stitch that are common choices for a heel flap; unlike reinforcing yarn, it is easy to use these in an area aside from the toes and heels, such as the ball of the foot, which is a high-wear area for some people. Finally, be sure you knit your socks long enough; a too-short sock will wear through in the toe more quickly than one which fits properly.
There are some preventative steps that can be taken after the sock is finished, also. If you didn't knit in reinforcing yarn, but you've changed your mind, it can be duplicate-stitched in, or woven in on the inside with a sharp tapestry needle. To weave it in, turn the sock inside out. Stitch in a grid pattern, catching the purl bumps on the back of each knitted stitch, and going back and forth across the area to be reinforced and then up and down as well. Areas such as the ball of the foot, which are tough to knit with a carry-along yarn in the round, are readily amenable to this sort of reinforcement. Duplicate-stitch reinforcement with the sock yarn is particularly good for areas where the foot could use a little extra padding, too.
A little maintenance will help you catch holes before they're a big problem. When you launder your socks, inspect them, looking for thin or frayed spots. If you find such a spot, go ahead and duplicate stitch over the area now, while you've still got the original yarn to guide your stitches; this is much easier than darning an actual hole. And for goodness' sake, if you find yourself doing this on the same spot on more than one pair of socks, go ahead and put some reinforcement in that spot on the rest of your socks too, because it's obviously a wear spot for you.
If a hole actually breaks through before you catch it, then you're going to need to darn the area. Darning is the process of creating some new fabric to cover the hole, and I'm going to tell you about three ways to do it: traditional darning, which is a species of weaving; duplicate stitch darning; and splicing in a new patch of knitting.
To do traditional darning, you'll need a sharp needle, some sewing thread in a matching or coordinating color, a tapestry needle, and something to create the darned patch, which can be more of your sock yarn or any similarly sized yarn, or substitutes such as embroidery floss if you no longer have any of the sock yarn. You may also want a darning egg, or a plastic ball or plastic Easter egg to substitute for one; you use this by putting it inside the sock, so it gives you a firm surface to work against, which is helpful for getting a darn that's not puckered. You'll start by putting in a reinforcing framework with the sewing thread. Go far enough into the fabric of the sock that you're not working in any damaged stitches, and using very small backstitches, sew a rectangle of thread around the hole with the sewing thread. You want these stitches to split the yarn of the existing stitches, so they're well-anchored; these will be the anchor of your patch. Now, switch to your darning yarn and your tapestry needle. Starting at one lower corner of the box of anchoring threads you just made, go under the reinforcing thread, draw a long thread across the box so that it's snug but doesn't pucker the box, and go under the reinforcing thread on the other side, and then come back to the first side, under the reinforcing thread, etc. Create a web of parallel threads, going back and forth from one side of the box to the other, and finish in one of the upper corners. Now, you're going to weave through this structure you just created. Starting at the upper corner, go under the reinforcing thread, and then go over the first strand, under the second, over the third, etc., until you reach the bottom of the box, and go under the reinforcing thread. Work back to the top, going over strands you went under before, and vice versa. Continue doing that until you have a solid woven mat of threads covering the hole, each anchored to the reinforcing threads, and then weave in your ends.
A traditional darn leaves a very strong patch, but you can definitely see it; it looks like weaving, not knitting. A duplicate-stitch darn, on the other hand, looks just like the surrounding knit stitches. If you catch the hole before the stitches actually break, it's simple enough to trace the existing stitches, however thin, but if they've already broken (unless it's maybe just a couple of stitches), you'll need to create a framework for the stitches that bridge the gap. You'll need the same supplies as for the traditional darning, above. Someone else has already made a great tutorial for this type of darning, so I'll just share that with you and go on.
The other great way to patch a hole so it looks just like the surrounding knitting is to knit in a patch; I'd probably use duplicate stitch for a little hole, and this method for a large one. To do this method, you'll need some of the yarn the socks were knit with (or a substitute in the same gauge), needles of the size it was knit with, your tapestry needle, and a pair of sharp scissors. Use the scissors to trim the hole to a rectangular shape, so that you have a column of completely undamaged stitches on either side, and a row of completely undamaged stitches above and below. You should have free stitches above and below the hole, in numbers equal to the number of columns of stitches involved in the hole; put those on two separate DPNs. Using the bottom stitches and the repair yarn, knit back and forth across those stitches until the patch is one row shorter than the hole. Thread your yarn onto the tapestry needle, and use kitchener stitch grafting to graft the patch to the sock stitches above. Then, use the tapestry needle to duplicate stitch over the outside column of the patch and the first undamaged columns of the sock, for every row, on both sides of the patch; using a sharp tapestry needle, and splitting the plies of the sock stitches, will help make sure the patch is thoroughly integrated into the sock. Weave in your ends, and you're done.
And finally, while we're talking about taking care of your socks, let's talk about washing them. If you do your laundry on cold, most superwash socks can just go right in the laundry; I wash and dry all of my superwash pairs this way. Non-superwash socks, however, should be handwashed and laid out to dry, and to tell the truth, many superwash socks will last longer and look better with this treatment as well. For handwashing socks, if you have other handwash items that you're doing fairly regularly, throwing the socks in with these is relatively little trouble, but what if you don't? Then, I recommend the Yarn Harlot sockwashing method -- it's fun!
What Stephanie does is to wear the socks into the bath (she takes baths -- the shower will work too). Lather them up while you're in there, rinse them out when you're done, and lay them out to dry. It's quick, it can easily be done at the next bathing opportunity after you wear the socks so you'll constantly have clean socks and not have to wait for laundry day, and your washing liquids are already conveniently located -- one of the best washes for wool socks is shampoo! Regular adult shampoo is as great for wool as it is for hair, and usually has the slight acidity that wool really likes; baby shampoo is less great, since its pH is designed to be gentle to eyes rather than to hair, but it'll do in a pinch. And cotton socks will do fine with bar soap, which is alkaline; if you've got a blend, though, go for the shampoo instead. What a nifty method! Stephanie is a genius.