(The arrows, point to yarn I wound in advance for seaming, before casting on––another little hint; all pics enlarge).
Twist, was "steam blocked"; meaning, I dampened––not soaked––the pieces first, using my iron's spray nozzle. Afterward, the stitches were set with blasts of steam from my iron hovering just over them.
Paying attention to the pattern measurements, I lined up the front edge of the left side of my cardi (wrong side facing). I pinned the bottom, top and center, then along the rest of the edge, no more than 3" (8cm) apart. Now, making sure that I kept the cable panel and rows straight, and continuing to pay attention to the measurements, I pinned at key points: the length from the bottom to the top of the neckline, the bottom width above the ribbing, the shoulder, armhole,* and across chest. Do not pin out the ribbing! It should retain its tightness. Once the left side was pinned, I aligned the lengths and widths of the other side to its mate. Any minor measurement discrepancies occurred while knitting, can be eased while you are pinning the dampened fabric, but remember––blocking doesn't work miracles. If the discrepancy is too great, e.g. 2" (5cm) too short, long, or wide, it won't work. You'll have to re-knit the piece to the correct measure.
*The armhole is a straight measure, from the edge of the shoulder, to the side edge; you don't measure along the curve.
Now, For The Fun Part
I held my iron over my cardi and applied bursts of steam to set the stitches. Don't dare press the fabric, or you risk flattening it;
then your finished piece will feel limp. An important note for
acrylic/wool mixes: The higher the percentage of acrylic, the less
steam you use. On 100% percent acrylic, use no steam at
all. Just pin, use a dry iron (no steam setting), and run the iron very lightly over your work.
When To Block
Some books say to block all the pieces at once. Me? I have a small board, and limited time, so that doesn't happen. Twist took four evenings: the back, the fronts, then each sleeve. If you pin out your piece to the proper measurements each time, it doesn't matter when to block (Wet blocking can also be done, one piece at a time).
What Method To Use––Steam or Wet, Sewn Or Not
My blocking method is determined by what I did to my swatch (remember that?). If I wash the swatch (to check growth, shrinkage or dye run), then I'll wash each piece, rolling out the excess moisture in a towel. Or, I do some laundry and drop it into the machine during the spin cycle. Afterward, either I pin out the piece and let it dry, or I steam it, or both; it depends on how it looks. For me, it's all about the end result, for that's what I and the public sees. Finally, I block before I assemble my work. It makes seaming easier; the pieces are already the correct measurements, and the seams aren't curling, the natural thing for knit fabric to do.
I hope this tutorial has been helpful, but remember that the ideal, especially for a garment, is to knit a large swatch––yeah, that's right––at least 8" x 8" (20cm x20cm). Then do whatever you're going to do to your piece, to the swatch, including the block. In the end, your sweater will love you for it.