When it gets cold outside, I have about three outfits that I normally go to, other than when I'm just being completely lazy and wearing tights with yoga pants, and an over-sized t-shirt.
Layers: Begin by a tank top or short sleeved shirt and go from there, then maybe add a sweater, with a cardiagan and a jacket with leggings under jeans with socks and boots. Trust me, you'll be thankful when you can take off layers for the scalding hot temperatures inside classrooms but can layer stuff back on to go through the arctic tundra like weather outside.
Always wear a scarf/hat. I'm naturally cold, so beginning in October when the weather even hints at dropping below 80 I'm in a scarf of some sort. There are so many different types/materials that scarves come in so you can always try different looks before finding a signature one!
Keep your summer clothes out during winter season. Now you may be looking at the screen and thinking, WHAT?! But really, wear a summer cut dress with a pair of thick leggings underneath and pair with a pair of thick high socks and you'll be good to go! Don't forget a nice jacket and cardigan as well!
Boots, boots, boots! I love boots, so when the weather begins to change, I'm all about breaking out the boots. During this time, it's really important to buy a nice, comfortable pair of boots and scotch-guard them if they are not leather so they don't get messed up easily!