First up, let's discuss the perfect pair to buy, assuming you can have only one pair in your closet. I would suggest you go for a pair in black leather with a slightly chunky heel that adds a little height, but isn't too high. A rounded toe and little-to-no "bling" will mean that you can reach for these with lots of different looks. I am also not opposed to a slight platform.
The pair of booties I just described will look great with skinny jeans*, trouser or wide-leg jeans, skirts and dresses. This pair is perfect for taking a fairly casual look up a notch and for making a potentially boring skirt and sweater option look a little more current.
*Few skinny jeans are narrow enough at the ankle to "tuck" into ankle boots, so if they're not a legging style, opt to roll the cuff to either meet the top of the bootie or show 1/2" of ankle.
Take a look at these combinations to get an idea of how to make these booties work for your wardrobe.