We all have our own rules, within certain bounds, about what is appropriate for what occasion. Other than major conventions (like not wearing a bustier top to church or an evening gown to the grocery store), the subtleties are highly individual. This is why you will see women dressed in a variety of ways when you go to a party. Some will be more dressed up than others, some will have short skirts and some, maxis. Some will be wearing pants and some, dresses. Some will wear a lot of jewelry and some, just a pair of earrings or none.
For the subtleties, it all boils down to personal taste, budget, and the image one wants to project.
And then there is the "sexy" factor: for example, I'd wear a casual, above-knee skirt with flats on a hot day at a Saturday B-B-Q party, but not with high heels on a job interview, if the interview is for a job in a business office. If the interview is as a hostess at a trendy restaurant and I'm in my 20s, then it would be OK depending on the restaurant ... and the skirt. lol. Is it a flimsy nightclub skirt or something that is acceptable for daytime. In other words, we all need to develop a sense of the message we give off when we wear certain things. It's really hard to pull off a, "Wow, look at that hot chick" look, and appear as this comes naturally with no attempt at attracting the opposite sex. If the message is that you're attempting to attract the opposite sex, then it signals that you are available and open to possibilities. And I agree, it takes a while for even GGs to learn this. I made a lot of mistakes when I was younger. In my early 20s, I bought a sexy dress for a fancy company Christmas party that looked great, but my husband thought it sent the wrong message. In retrospect, he was right. He was the boss and I was the boss' wife and it was an office party, not a group of friends going to a jet-set party on a yacht. The dress looked something like this, except it was shorter in the front than the back.
Jewelry is purely a question of personal taste (although I agree with Allsteamedup for contemporary fashions) and so is what top goes with what skirt, although it doesn't work to match a winter top with a summer skirt, or colors/styles that clash, or a diamond necklace with a pair of shorts ... but you've been dressing long enough to have developed your own sense of what works and what doesn't? Also, IMO it is so important for people to dress for the bodies they have and not the bodies they want to have. We've all seen men and women dress in clothing that is too small or age inappropriate (i.e. you won't see middle-aged women wearing this, this, or this).
This is a great article on how to dress your age, IMO:
http://www.harpersbazaar.com/fashion...your-age-0415/