QueenCadbury frugal posed about contrast and planes on 2nd April so I've c&p below:
General principles of dressing
1 The principle of similarity - create visually pleasing harmonies by repeating a shape, form or shade: the curve of your cheek, your legline, your natural colors, etc
2 The principle of contrasting - add visual interest by adding contrasting elements.
Example 1, principle of similarity and contrast. I'm tall and quite thin. It's a good thing in moderation, but if I overdo enhancing similarity, I look like a Holocaust survivor. So I enhance certain parts of my shape (I tend to show my legline; I repeat my natural colors in my outfits) but I also introduce contrasts (I'm strongly vertical, so I add horizontal elements to my outfits). Example: a tall thin woman I saw this morning. She wore tight trousers and riding boots (=strong vertical element) teamed with a voluminous fur-collar parka (adding horizontality). She looked balanced, not like a Giacometti sculpture.
Example 2: I'm pale and low-contrast. If I dress completely in beige, I'm invisible. Strong medium-intensity colors (red, green, blue) make me more visible and enhance the milky tone of my skin. People have naturally different levels of contrast. Take a black-and-white picture of yourself (=Photoshop your picture) and observe the contrasts. Do you see white and black a la Nigella Lawson and Snow White? -> high contrast. Do you see clear contrasts but everything is in shades of gray - > medium contrast. Is everything quite monotonous and low in tonal variance -> low contrast. If you are naturally high contrast, repeating this grade of contrast in your outfits will work (=you can use black and white). If you are low-contrast and wear high-contrast outfits, your clothes will swamp you and you will look drab and insignificant in comparison - you will achieve "high contrast" by using tones much closer to each other. If you are low-contrast, Google Sarah Jessica Parker and study her outfits. Can you see how she respects the principle of similarity most of the time (hair, skin, lips, many of her clothes) but also skilfully employs the principle of contrast (her eyes are usually the contrasting element). I'm very low contrast and a good "black and white" for me is steel gray + oatmeal or cream. I can either respect it and go for a relatively muted-color outfit (principle of similarity) or add visual interest by going for contrast (add bright lipstick, bright colored clothes). Because I tend to look bland, I always make sure that my brows and lips are clearly defined (this also increases horizontality - I tend to be over-vertical otherwise).
How to define your leading visual plane
Vertical - tall, thin, stick-figure like, long-limbs - you can emphasize and repeat your verticality by adding vertical elements but will balance your proportions by introducing horizontal elements. Full skirts, horizontally striped tops, rectangular necklines, bulkier tops or voluminous trousers or sleeves. Do this to just one part (respecting the 3:5) of your body.
Horizontal - short, wide - introduce vertical elements to your outfits (create vertical visual cues by the use of buttons in jackets, long straight trousers, pleats, topstitching, etc; avoid an excess of horizontal cues)
Diagonal - are you X-shaped (hourglass), Y-shaped (inverted triangle) or do you have prominent cheekbones, sloping eyes or a heart-shaped face? Repeat diagonal elements throughout your outfits: wrap dresses, bias-cut clothes, V-necks repeat and enhance your natural diagonal planes.
Average - most people are average. Not particularly tall, not particularly wide, not particularly diagonal, just average. In your case, pick out 3 to 5 parts in yourself that you particularly like. Then use the principles of similarity and contrast to showcase them (=repeat the shape of that body part in your outfits; highlight them by using the principle of contrast).
Curvy - If you are curvy, study women who dress curves well - Jennifer Hudson, Queen Latifah for example. Kirstie Alley is very interesting because she can get it spectacularly wrong (google her!). You can learn what works and what does not by observing her. I know a few XL models irl. They are off the charts sizewise (not size 14!) but look stunning. One of them repeats her sinuous curves in her outfits and uses sensuous silk jersey and heavier cotton jersey to make her top part look even more voluptuous. She buys her skinny jeans from 'urban' brands and vacuum-packs her bottom - she gets cat calls on the streets. Another friend makes her brown eyes and creamy skin the visual focal point of all outfits - you never really notice the rest of her body. Blogs featuring curvy women are worth studying - you can see what works and what doesn't and then try out the looks you like best.