I feel like I'm taking the first steps towards something like this, however, as a retail-working student I don't want to have a uniform of sorts yet simply because I'm not in a professional environment so I like the flexibility my life allows me. I have however had most of my clothes for 2-3+ years, and they're still perfectly appropriate/stylish because of these rules. For the record, everything I own is black, various shades of grey, (not much) white, deep navy blue, and deep foresty green.
My main rule with shopping/things I own is that I basically want to be able to wear anything with everything. Both colour-wise and shape/style. Any sweaters I own have to layer as nicely over a dress as they must work with trousers or a skirt, and every blouse or shirt has to work with trousers/skirts. I like to have shoes that work with everything as well, but also make me feel like everything has been pulled together by them. I find that keeping the versatility with everything I own makes styling myself so easy, layering even easier, and really, if I'm in a hurry, I can grab virtually any two things, throw them on in whatever order I choose, and then leave.
Even things that may not seem like they could go together - cropped turtleneck and a slip dress have proven me wrong. However, by this rule, I get rid of anything that proves itself difficult to style, and if I can't find a way to make it work at any time in a two-week period, it's donated/sold/returned (unless I feel it can have potential with a better pair of jeans). Extra points go to micromini shift dresses/t shirt dresses that double as shirts that I can wear with a midi skirt/skinnies.