When you are working a cable, the background stitches are usually worked in reverse stockinette stitch--purl on the right side and knit on the wrong, like you laid your's out in the first row.
The cable itself is worked in regular stockinette stitch, so your example would be
Row 1 - p4, k4, p8
Row 2 and all even rows- k8, p4, k4
You would do the cable cross every 4, 6, 8, rows--however you want it to be.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry