I had the idea for these shows because I made a golf-club cover for someone a while ago (not my dad, he actually framed the covers I gave him because he's afraid of messing them up) and he said it sprung holes almost right away. It could have been a split stitch, I guess, but it really looks like an act of a cat to me.
When darning, first stabilize the patient. I like to use small needles and/or dental floss to thread through the live stitches, starting with the lowest row that has a loose stitch. The dental floss is more flexible, but, to me, the small needles make it easier to hold the structure. On the other hand, a whole lot of dental floss can fit in your knitting bag and it's much cheaper than having extra needles around all of the time.
If that loose stitch has ladders over it (stitches that have slipped in the same way as if you dropped a stitch off the needle), I pull the stitches up with a crochet hook.
Now, I have brought up the loose stitch and isolated the lowest place in the knitting that is a full row without a hole in it. So, I take my darning needle and some matching yarn and a start a row of darning two stitches from the edge of my hole (leaving a tail to be darned in, too, in its time).
The stripes in this example are a good thing for us. It makes it easier to see that, while it looks like I'm actually darning one row up from where I should (or that I'm too close to the row of black) you have to remember that the "loose" stitches are a row, so be sure that you are working the correct row. If you're not, you can always jump rows when you get to the live stitches. So, I only have to darn one row of gold before I get to black.
You can see, above, that I screwed up. I accidentally darned in the wrong direction and made a purl stitch instead of a knit stitch. This is ok, because if you're paying attention, you can notice that, simply undo it, and learn more about how to do it properly.
So, we see that this hole can be fixed with one row of darning, although it seemed much worse before, because of a dropped stitch. So, it probably was just a single stitch that went south. Just goes to show - one stitch can sometimes cost nine darn photos.
This is the same idea, in two rows of white:
Now, a little bit of slight-of-hand. I darned this hole, but then found a mistake in one of the stitches - I had twisted it when I made the darn. Instead of picking it out, I darned over it again, strengthening my join and hiding my mistake.
