Top to bottom: Jane Birkin, Madonna, and http://www.garnethill.com/.
Here are some easy ways to emphasize our natural vertical line and the "line of beauty" in the female form. These aren't "rules." Just ideas I've learned that work and help me feel good about what I'm wearing.
1. Choose simple, classic pieces in updated versions and without a lot of doodads that slow down the eye’s progression up and down the vertical line. All three of the examples above are doing this.
2. Pick a monochromatic or "tonal" combination for top and bottom (tonal means the pieces are the same darkness or lightness). This combination can be used like a backdrop for colors and more individual pieces. The model in the middle is doing this because her sweater and pants are the same color; but it would also work if she had dark jeans on.
3. Decorate only what we want to emphasize, because eyes will go there. I think especially with Madonna, our eyes go right to her hair.
4. Wear clothes that fit our individual body shape, and are neither clingy/tight, nor sacklike. Everyone above is doing this, of course, because they have stylists. They have vertical line, and you can see the line of beauty. Madonna's coat is cut to show her waist, and Jane Birkin has cinched in her pieces with a narrow belt. See my first post ever--"Do This First: Read The Pocket Stylist by Kendall Farr."
5. Notice our widest points and try not to emphasize them with horizontal lines. (On me, it’s my hips. This means my shirts don’t end right at my hips, creating a horizontal line there.)
6. Wear our pants long enough to hit instep, or longer if you want to wear heels. Madonna's pants are long and she has heels on, which also make her more vertical. Her pants are probably too long to be practical, but we can be aware of covering our socks.
7. That said, have socks match pants, not shoes. If pants and shoes are a similar tone this will also create a longer visual line.
8. Choose vertical accessories like a longer scarf or necklace.
9. Wear v-necks. Jane Birkin is doing this.
10. Have on hand a "skimmer"-type cover like a duster or long sweater. See black sweater from Garnet Hill above. This idea is one of my favorites, and one that got me through an entire winter of clothing identity crisis.
11. Be careful with horizontal stripes. They work on the model from Garnet Hill because they're small and her overall image is still vertical. I recently read that small horizontal stripes can actually draw the eye up and down and therefore are a good choice for creating a longer line. I ran right out and found a small-striped top at my favorite thrift store.