This is the sock pattern I fall back upon when I haven't a clue what I want to knit for a sock or when I'm looking for something basic. It's a simple K2, P2 ribbed sock in which I carry the ribbing down the instep.
Yarn: ~400 yards of your favorite sock-weight yarn. I've used Socka, Sockotta and Marks and Kattens Clown with this pattern.
Needles: For me, I use a US size 2 needle and I use double points, not circular(s). I also like sets of five needles rather than sets of four needles, but that's just my preference. You should pick the appropriate needle size you need to meet the gauge.
Gauge: 7 1/2-8 stitches to the inch in stockinette stitch.
Cast on 64 stitches and K2, P2 around for 6".
Knit heel flap on 32 stitches. Sl1, K1 on right side rows. Sl1, purl across on wrong side rows. I make my heel flaps 2 to 2 1/2 inches long. I also center the heel flap so that there is one purl stitch on each end. This causes the ribbing on the instep to be centered on the foot. It's a minor detail, but I'm really picky about having designs centered. My eye picks it up when they're off-center and it bugs me.
To turn the heel, knit to the center plus one more stitch, SSK, K1. Turn.
On row 2, slip 1, then purl across until 31 stitches remain on the left needle, P2tog, P1. Turn.
Sl1, knit until 1 stitch before the gap, SSK, K1. Turn.
Continue until all the stitches are used up, knitting or purling the stitch before and the stitch after the gap together and slipping the first stitch of each row. You should end having just completed a right side row, even if you have to knit back across.
When I pick up the gusset stitches, I pick up only one leg of the edge stitch and I don't count how many stitches I pick up on each side. I pick up each slip stitch and an additional stitch between the heel flap and the instep. When I pick up and knit the stitches, I twist them. In my opinion I think it looks neater to twist the stitches. Try it untwisted too and see what you like best. It's your sock.
Pick up the stitches along the first side of the gusset/heel flap, then K2, P2 across the instep and pick up the stitches on the second side of the gusset/heel flap. At this point, I start to think of the center of the heel as the beginning of a round. Oddly enough, I usually put all of the heel stitches on a single needle, instead of dividing them, and I think of the heel stitches as the beginning of the round. The other three needles hold the first set of gusset stitches, the instep stitches and the second set of gusset stitches, respectively. I decrease the gusset stitches every other round, knitting to three stitches before the end of the first gusset needle and K2tog, K1. Then P1, *K2, P2 across the instep*, ending K2, P1. On the 2nd gusset needle, K1, SSK, then knit to the end. For the 2nd round, knit even with no decreases. Continue until you're back to 64 total stitches. Once you're back to 64 total stitches, continue knitting the sole of the foot in stockinette and the instep in K2, P2 ribbing.
Knit even down the foot until about 1 1/2 inches shorter than your foot length. On my foot, this is at the base of my big toe. Divide the stitches into the top and bottom of the foot. There should be 32 stitches in each half. Knit one round plain. Remember, the heel (or the middle of the bottom of the foot) is the beginning of the round.
Knit to three stitches before the end of the sole stitches. K2tog, K1.
On next needle: Knit 1, SSK, knit to end. (approx partway across instep)
On third needle: Knit to 3 stitches before the end. K2tog, K1.
On fourth needle: K1, SSK, knit to end. You should now be back at the beginning of the round, in the middle of the sole.
Knit all the way around plain.
Continue alternating these rounds until approximately 12-16 stitches remain. Either graft the toe or turn sock inside out (with needles in place) and do a three-needle bind-off. As tricky as it sounds, I find it easier to turn the sock inside out and do a 3 needle bind off than to graft the toe closed. It looks nicer too and if I need to re-knit the toe, it is incredibly simple to pull it out and re-do.
Weave in the ends and you've got a finished sock! Now you just have to go make a second one.