Cast on 28 stitches + 2 extra stitches
1st Row (right side): Purl
2nd Row: K1,*work [k1,p1,k1] all into next st, p3 tog; rep from * to last st, k1
3rd Row: Purl
4th Row: K1,*p3 tog, work [k1,p1,k1] into next st; rep from* to last st, k1.
These 4 rows form pattern.
Continue in pattern till you reach the length you need then cast off.