Summarize:

If you're just making a sample swatch, chain (ch) up 17 stitches. For a larger swatch or blanket, chain 34 or 51 stitches which are multiples of 17. Wrap the yarn around your hook and insert it into the fourth chain from your hook. Continue to yarn over and pull through the loops on your hook to make a double crochet stitch. Make 1 double crochet stitch in each of the 5 chain stitches across the foundation row. Then make 1 dc stitch, chain 2 stitches, and make 1 more dc into the next stitch. Keep working across the row by making 1 double crochet stitch into the chain stitches. Skip the next 2 chain stitches and double crochet 1 into each of the next 7 chain stitches. Then dc 1, chain 2, and dc 1 into the next chain stitch. Dc 1 into each of the next 7 chain stitches. Keep repeating this pattern until you reach the end of the row. Flip the work over so you can begin crocheting your first real row in the zig zag pattern. Make 3 chain stitches and skip the stitch closest to your hook. and dc 1 into the next 5 stitches. Decrease the number of stitches in this row by double crocheting 2 of them together. Then you'll need to double crochet 1 stitch into each of the following 5 stitches. Insert your hook into the next 2 chain space and make 1 double crochet stitch. Chain 2 into the same stitch and double crochet another 1 stitch into the same stitch. This will form the point of the zig zag. Make 1 dc stitch into each of the next 7 dc stitches. This will bring you across the other diagonal side of the zig zag. Then skip 2 double crochet stitches and dc 1 into the next 7 dc.  Remember to double crochet into each of the 7 stitches across the row. Insert your hook into the next dc stitch and make 1 double crochet stitch. Chain 2 into the same stitch and double crochet 1 more stitch into the same stitch. To work the zig zag pattern, keep repeating: Dc 1 into each of the next 7 dc stitches, skip the next 2 dc stitches, dc 1 into each of the next 7 dc stitches, and then dc 1, chain 2, and dc 1 into the next stitch. To finish the row, make 1 double crochet stitch into each of the next 5 dc stitches. Join together the next 2 stitches and dc 1. Turn the work to make another row, if desired.
Make a foundation chain that's a multiple of 17. Insert your hook into the fourth chain and make 1 double crochet stitch (dc). Dc the next 5 ch stitches and dc 1, ch 2, and dc 1 into the next stitch. Dc into each of the next 7 chain stitches. Finish the foundation row by double crocheting and skipping stitches. Turn the work, chain 3, and skip the first stitch. Dc the next 2 stitches together (dc2tog) Insert your hook and dc 1, chain 2, and dc1. Dc into 7 stitches, skip 2 dc, and dc in the next 7 stitches. Dc 1, chain 2, and dc 1 to make another zig zag point. Continue to crochet in zig zag pattern until you reach the last 8 stitches. Dc 1 into the next 5 dc stitches and dc2tog the next 2 stitches.