In the manga, Ami always dresses in very elegant and feminine clothes, when not in school uniform. Her clothes often have flowery patterns and long lines, and match. I love her outfits in the manga, particularly at the start of SuperS, and some of the outfits Takeuchi-san draws her in for artbooks or covers.
The anime seems to credit most everyone with a complete lack of fashion sense, particularly Ami. A lot of the outfits 
they put her in are hideous, not to mention the fact that often her hair is drawn like a skullcap, with no shape, flat to her head. Other times her hair can look really pretty, but for the most part the clothes she is shown in are color-mismatched and not very stylish; prudish or victorian style (large collars, long sleeves, and so on). She often wears oranges and yellows, possibly because they contrast so much with the blue hair she has.
In PGSM, she often dresses very feminine and staid, but has shorter skirts, and slightly more stylish, but not risque. She 
wears short pleated skirts, blazers, and often very thick jackets, and carries the largest purse of any of the senshi, presumably stocked up with all her school books. She also makes a point of wearing glasses she does not need, so that she feels more secure, perhaps this is also why she wears her hair the way she does. She's very shy, and retiring, and not confident in herself at all. The more she is with the other inners and becomes sure of herself, the less she's wearing her glasses, however. She has also taken to wearing her hair, occasionally in twin french braids on either side of her head rather than pulled so strictly back into the half ponytail. She usually wears whites, pastels; rosy pinks and blues, when she's not wearing school uniform.
Although in some of the mid-season episodes during the time of Darkury her style changed. She would wear her hair down, and not wear her glasses, and her clothing was more punk/gothic in style, wearing black jackets over white sweaters, or dark blouses and ties, rather than the normal 'pure' and 'innocent' clothing, a reflection on her change in personality.
Once she was restored to normalcy her personal clothing styles reverted to their usual ways, although in episode 30 when the senshi are helping Mako choose clothing for her date, the clothes that Ami has stored in her camera phone, are apparently rather risque in the mind of the other senshi.
