The herringbone stitch consists of two rounds that get repeated throughout. At the end of the round, you move the stitch marker (SM) differently, depending on which round you are on. This is done to ensure that the switch between the rounds stays in roughly the same spot, instead of moving around the work.
The two rounds are:
Rnd 1: *K2tog dropping only the first st off the left needle, and keeping the second st on the left needle*; repeat between * * to one st before SM, slip the st from the left needle to the right, remove SM, slip st back to the left needle and work a k2tog with the last st of the current round and the first st of the next round. Again, drop only one st off the needle, and replace the SM.
Rnd 2: *K2togtbl dropping the first st off the left needle, and keeping the second st on the left needle*; repeat between * * to one st before SM, slip the st from the left needle to the right, remove SM, slip st back to the left needle and replace SM. This now becomes the start of the next round.
This pattern can be worked over any amount of stitches and rounds to make exactly the object that you want.