I agree it is a bit of a problem not having sisters, or possibly a mother to guide you although I know our daughter sort of rebelled over what we thought was fashionable and what she did
For myself I read women's magazines, and people watch. It's a simple way to pick up on fashion trends and tips. Also when out and about check out the clothing stores and their store front displays as they usually have the current trends on display as well. They also show what goes good with what, how to mix and match etc...
Buying a few key items can go a long way into expanding your wardrobe and fashion sense. For example having three basic plain skirts of a cut that is flattering to your figure (I look better in "A" line skirts), cut just above the knee in brown, navy and black and three pairs of pants of similar colours. With these you can buy a whole lot of tops in different colours and styles to mix and match.
Jackets are also a favourite as I can wear simple tank tops underneath and when mixed with the skirts or pants you expand your wardrobe quite a lot, add a couple of pairs of matching shoes and you're good to go.
Casual wear is a lot easier, shorts, tee's, running shoes, slides, and flip-flops, and of course don't forget the jeans, a girls gotta have jeans
We have a strict dress code at work so I have to ensure that I have a good selection of clothing and outfits that comply with the regulations. So my work wear is somewhat dictated. But while developing your own fashion sense can be daunting it gives a girl the chance to shop. When I first started buying my own cloths I hit the second hand clothing stores. I know that this doesn't appeal to everyone but it's a cheap way to find out what looks good and what doesn't and if you make a mistake then you haven't wasted much.
As far as those fashion traditions go such as the one on when you can or cannot wear white. White is one of my favourite colours (Is it a colour?) and I wear it when it suites, and so do many other women. Another example is the tradition of wearing black at funerals a sign of morening in the west, white in many oriental countries. More often than not you will find many wear a variety of colours. I would suggest you go with what makes you feel good and not by some ancient traditions
Steph
