Knitting the Afghan
In order to knit a shell stitch afghan, begin with the cast-on you prefer. To figure out the cast-on, determine the number of pattern repeats you need based on your swatch. You did swatch, didn't you? Good! So let's call your pattern repeat number "X" and do a little knitting math.
Cast on: 7X + 10. In my case, I'm knitting my afghan kitten-sized for Gary the Cat, the newest addition to our family. With my worsted weight and size 9 needles, I cast on 66 stitches (8 pattern repeats times 7 is 56, plus 10 is 66).
After you cast on, knit your afghan in the following manner:
Rows 1-4: Knit all stitches.
Row 5: K4, PM, K across to last 4 sts, PM, K4.
Row 6: K4, SM, P to last marker, SM, K4.
Row 7: K4, SM, K2, *YO, P1, P3Tog, P1, YO, K2.* Repeat from * to * across to last marker; SM, K4.
Row 8: K4, SM, P to last marker, SM, K4.
Repeat rows 5-8 for the body of the afghan.
Final 4 Rows: K all stitches. Remove markers as you bind off.
Thread your yarn tails onto an embroidery needle or other large eye blunt needle and weave in your ends.