Work one round in plain knit stitch. Then work an increase round. To approximate a circle, I increased once on each needle. Rather than subject you to more of my substandard photos, I'll direct you to a couple of good resources for learning to increase. This site
has clear drawings of each step. I used what she calls the "Right Increase". Scroll down to see it. The same increase is shown in video form on this page
. Look for the "Knit Right Loop" increase.
For each needle in the first increase round, I knit one, make one (that's the increase) and then knit one more. At the end of that round, I'll have a total of nine stitches. Knit one round plain, then another increase round (K1, M1, K to end per needle) for 12 stitches total.
: on the plain rounds, give the yarn a little tug on the second stitch on each needle. This will compensate for the gaps that appear between needles. It's not really necessary on this tiny project, but it's a good habit to get into.
After a few rounds, turn the work over and pull the tail in the center to tighten up the knot and bring everything together. Work a couple more rounds and test for fit on your earbud. When you can stretch it so all three needles are on the back side of the 'bud, that's the right fit. For me, I got there when there were 18 stitches on my needles, but your mileage may vary.