The biggest thing I've found is to not stop riding. If I just keep riding all fall and into the winter, then my body adjusts and I really don't need to do anything too radical. If I were to not be riding at all and then suddenly start riding when the temps were cold, then it's a big shock to the system. Here's the general way I dress:

55 degrees and above: regular cycling clothes - shirt and shorts, etc.
35 - 54 degrees: Add full fingered gloves, headband and either a light jacket or long sleeve sweatshirt.
20 - 34 degrees: Add long pants and heavier gloves when in the lower half of this temp range.
10 - 19 degrees: Change my lower shirt layer to long sleeved. Add my balaclava and warmer shoes/shoe covers.
9 degrees and below: Add a base layer of thermal underwear (both shirt and pants).

That's it. Nothing too technical or anything weird like wearing a full parka. This setup has taken me down to -14 F (wife complains if I ride when it's any colder, so I try to keep her happy.)

Dress so you're chilly the first couple miles. Once you get warmed up on the bike you'll be about right. If you dress so you're toasty warm when you first head out, once you get going you're going to sweat and actually make yourself colder in the long run. In my experience it's more common to overdress for winter riding than to underdress.