Basically, it goes like this: if you have a small frame, you will be most flattered by delicate things - if you are large framed, you need to think bigger. So, let's start at the top. Take, for example, the wooly hat. If you have fine features and sleek hair, a baggy beret can make you look like a mushroom. On the other hand, bigger hats will balance out a bigger body and be in proportion to big hair or a rounder face. A large lady in a juliet cap is wont to look like a cherry on top of a cupcake. Hair too, then. None of these rules are hard and fast, and if you love a look that is the number one most important thing, but bigger hair looks better of bigger people - it's very hard to pull off a gamine crop unless you're elven of features. It works the other way - big hair on a petite frame and you're likely to look a bit cartoonish. It's even true that very long hair looks best on tall people: and here I'm guilty of ignoring my own advice. If you're short, too many long straight verticals can draw the eye too far down and make you look dragged down.
Jewellery - and by and large it's the same rule. Fine chains are hard to wear if you're larger because they look overwhelmed by the surrounding flesh, whereas big statement pieces can look like they're wearing you if you don't have the frame to balance them out. Of course, you might be a tiny size eight and have quite chunky hands - go for jewellery that suits the part of the body you're wearing it on. It's not quite as simple as that, though. Beware bracelets and chokers! Anything chunky cinching the thinnest part of you (wrist, ankle, neck) actually makes it look wider. It's the same reason that wrist-length sleeves are less flattering than three-quarter ones. So look for larger circumference bangles or bracelets that will sit past the wrist, onto the hand, or up the arm a little: it's a much more flattering look.
Patterns are simple. The bigger you are, the bigger the pattern you need... but: keep patterns simple as a big busy pattern on a big body will make you look like a sofa.
Belts follow the same theory, except that you also need to consider the weight and thickness of the fabric(s) in your outfit. Sometimes it can be nice to juxtapose floaty and flimsy with chunky and industrial, but for a more elegant look you'd keep them in proportion. There's often a fashion for big belts, worn by slim ladies - that's fine, but they should then be worn on the hips. Trying to cinch a slim silhouetted outfit on teeny frame at the waist with a big belt can make you look like a weightlifter. Sorry.
Then, lastly, shoes - or more specifically, heels. In theory, you'd want to leave slim heels to slim girls (a skinny stiletto beneath a plump calf can look like one of those balloons-on-a-stick they have in McDonalds for the kids) - and as far as possible you should aim for this, but more importantly, if your leg has curves, so, ideally should your heel, and that's more true the thinner the heel is. Platforms and wedges also suit more substantial calves more than they do slim ones - remember my chicken-legged friend? She should avoid a blocky heel lest it look wider than her calf. Again, the actual proportions of the body part are important too: I have size 3 (36eur/5US) feet, but they're broad and so delicate strappy sandals wouldn't suit as they would if they were more narrow. If your ankle is significantly narrower than calf and foot (mine look like the knots between sausages) again, avoid any straps that are right on the ankle. Ties up onto the leg or down on the foot are far better.
Massive apologies if you already knew that stuff, by the way. It's the sort of thing that I feel like I've always understood, but people tell me quite often that they find these types of post useful.