Okay, let's get this thing started. Twice this week I've had knitters tell me that they were scared of yarnovers, and afraid to try any patterns that included them, and I've helped a couple of other people figure out pattern problems that were caused by incorrect yarnovers, so this is plainly a topic on which there's a lot of confusion.
One big source of the confusion is that there are a lot of bad instructions out there. One popular way to tell people to do a yarnover is to tell them to move the yarn to the front, and then from that position knit the next stitch. This does, in fact, cause a yarnover to happen, but it's a horrible way to teach it.
Why? Well, three reasons. One, it gives the strong impression that knitting the next stitch is part of the yarnover, and this is wrong. Two, it leaves a person with no idea whatever what to do if the stitches before and after are anything other than two knits. And three, it completely glosses over the loop over the needle, which is the very essence of a yarnover.
Can I do better? Yes, I think so.
First, what is a yarnover? It's a simple thing: just a loop of yarn that goes over the right needle. It should be oriented in the same way that other stitches are oriented, which for most people means that it needs to come up the front of the needle first and then down the back. It does not include knitting or doing anything else to the next stitch on the needle, and in fact does not use up a stitch from the previous row at all. It does increase your stitch count for the current row by one, so if you do not want your piece to get wider, you need to balance it with a decrease; if you do want it to get wider, of course, that isn't necessary.
Now that we know what a yarnover is, how do we do it? The yarnover itself is accomplished by simply flipping the yarn over the needle, but there may need to be a step before and/or a step after, depending on what the preceding and following stitches are.
If the preceding stitch is a knit (and for purposes of this, anything that is a variant of a knit, like a k2tog, counts as a knit), you need to move the yarn between the needles to the front, because the yarnover starts with the yarn in front. If the preceding stitch is a purl (or a variant of a purl), then you don't need to do anything, because the yarn is already where you want it.
Once the yarn is in front, just bring it over the top of the right needle to the back. That's your yarnover! Wasn't that easy?
Now, if the following stitch is a purl, you need to move the yarn between the needles again, to the front, so you're ready for that following stitch. If the following stitch is a knit, you don't need to do anything extra, but are ready to work that stitch.
So, three little steps: move the yarn forward if it's not already there; flip it over the right needle; move it forward again if you need it to be forward for the next stitch. Ta da! And now you know how to do a yarnover, regardless of what the stitches around it are, and without screwing up your stitch counts.
Be sure to read the next couple of posts, which will explore a few other aspects of using yarnovers in your knitting.