My initial reaction was to divide into 8 sections of 10 sts each and I think that is what the pattern is aiming for. To do that, knit 8, k2tog around. You'll do this 8 times, total. Usually the next row is plain knit and the following row would be k7, k2tog. Those last 2 rows repeat (decreasing the number of sts between the k2tog by one on each decrease row).
You really don't need to use markers, but if you'd like, it will make sure that you don't knit too many or too few sts between the dcreases.