To work a sample like this one, you'll need two colors of yarn: color A and color B. I used Cascade 220 wool yarn in navy and silver heather. You can use any colors or fibers you like.
Using color A, start with a foundation chain of any number of stitches.
Row 1: Single crochet in the second chain from your hook, and in every chain stitch across the row. Work a turning chain and turn the work.
Row 2: Work one single crochet stitch in the back loop of each single crochet, all the way across the row. When you get to the last stitch in the row, insert your hook as usual and draw up a loop. Then switch to color B by drawing through a loop of color B to complete the stitch. When you do this, make sure to leave a long tail of color B for weaving in later.
Evaluate whether you want to carry your yarn up the sides of your work. You can do so from this point on; just drop the unused yarn and pick it up again later when you need it next.
Then work a turning chain and turn.
Row 3: Work the entire row in single crochet, again working only in the back loops.
Row 4: Work another row of single crochet in color B, continuing to work only in the back loops. When you get to the last single crochet stitch in the row, switch back to color A.
Continue alternating between working two rows of color A and two rows of color B.