I’ve met several teachers that have the strong belief that ever sweater should have shaping. I cannot say I totally disagree, but there are some sweaters I would not put shaping in. Something that is going to be so big on me that the shaping won’t matter, would not get any shaping. Like a comfy sweater for home.
The smallest amount of waist shaping can make a huge difference though; taking a garment from box shaped to beautiful. Even men’s sweaters could use a little bit of shaping going from the shoulders/chest to the waist.
One of the most common kinds of shaping involve increasing and decreasing stitches along the sides. My absolute favourite pattern’s waist shaping is from the top down and you end up decreasing for the waist and when you increase for the hips, you add more stitches than you had for the bust. It is really quite clever because this sweater fits me perfectly. When you think about it, that shaping technique makes a lot of sense. If you happen to be a bit bigger on top then around the hips, add a few more stitches in the bust.
If there is no shaping in the pattern you are going to have to use your common sense to add it in. I would look at patterns that already have shaping and try to apply it that way. Read at least two or three and you should get the general feeling for how shaping is inserted into the pattern. I would highly suggest you use a pattern you are familiar with, that you have either knit before or have tried on a finished product. I think the shaping of a garment is an extremely personal thing and different designers do it different ways.
If you have never done any shaping before, find a pattern that already has it included. The best way to get to know a technique is to try it! Usually, it is best to try it in a structured environment if you’re on your own. The pattern comes in handy for accommodating extra stitches and keeping track of them.
For something a little less invasive then adding in or taking away stitches, you can just change the needle size you are working on. Patterns have you swatch for gauge so your knitting will match theirs and the sizes will be accurate. If you go up or down a needle size, the gauge and garment size changes. For shaping, you are purposely changing the gauge for a small portion of your garment. For a waist, you would make the needle size smaller while you’re knitting through that section. As I have never tried this technique for myself, I would suggest not going too extreme in the needle size changes. You don’t want comical shaping that would only work if you were a barbie doll or ambitious corset tightener.
There were not a whole lot of videos about waist shaping so I am providing a link to Amy Herzog’s blog. This is her article about waist shaping and her Fit to Flatter program always uses it. Here is a link to a brief synopsis of the Fit to Flatter, I would highly suggest giving it a look! I am taking a couple of Amy’s classes in October at Vogue Knitting Live Chicago and I can’t wait!