I use the garter tab cast on for most of my top down shawl designs like Daybreak, Herbivore, Akimbo, Pogona, and the 2011 Mystery Shawl: Earth & Sky.
The stitch counts in the photo tutorial below represent the exact same instructions for the beginnings of Transatlantic, Pogona, and Earth & Sky. You can use the same tutorial for my other shawl designs, but the cast on number or garter stitch rectangle length may be slightly different.
1. Cast on 3 stitches. My default cast on is the long tail method, but just about any cast on will be fine here.
2. Knit 6 rows. At the end of last row, do not turn to work other side. Sometimes this little rectangle can look wonky, especially when worked with fine yarn. Give it a little tug and make sure it is not twisted for the next step.
3. Rotate piece 90 degrees clockwise so that you are looking at the long side of the garter stitch rectangle. Pick up 3 stitches (1 in each purl bump from the garter ridges).
4. Knit into those 3 picked up stitches. The picked up stitches can be picked up all at once as illustrated in the photo above or you can pick up and knit those 3 stitches one at a time.
5. Rotate piece again clockwise so you can pick up 3 stitches along the cast on edge. This can be the trickiest place to pick up stitches. Just locate 3 strands of yarn along that cast on edge to pick up.
6. Knit into those 3 picked up stitches. You now have 9 stitches scrunched up in a little blob.
This photo shows those 9 stitches spread out a bit more.
You are now ready to begin the first rows of the shawl.