As the temperatures drop, we return to seasonal issues of ice dams, snow, and a furnace that seems to be constantly on. The "Ask This Old House" crew recently did a great episode addressing many of these issues (see below).
Most homes built in the first half of the 1900s suffer from ice dams, unless a prior owner addressed these issues (which is unlikely...). There are many great resources that explain why ice dams occur, so we will focus on how to either prevent them or treat them.
Preventing ice dams is the best long-term solution, but of course it is also the most difficult and expensive. The goal is to prevent heat from escaping through your attic and warming the roof surface, where the snow melts. It then trickles down to your eave or gutter, there it freezes and creates the ice dam. So to trap the heat inside your house, you need to air seal and insulate. Unfortunately this sounds easier than it is.
Air sealing your attic floor generally requires removing all of the existing insulation (hopefully you have some, and ideally a lot). Then all of the gaps and openings (electric boxes for ceiling lights, bath fans, etc.) are either filled or "boxed in". This entails building a small box, often out of rigid insulation, to cover the electric box or can light, and then sealing around it. Just piling on more insulation isn't enough - air sealing is a critical step (for more read this article). But then pile on lots of insulation. Blown cellulose is a good option and a layer of about 18 inches will get you up to about R-60.
If you currently have access to the attic and store things there, preventing you from adding insulation, you may want to find a different storage place. Even just the door or hatch to access your attic is leaking a lot of heat. You can get highly-insulated attic access doors if this is the case.
If this is too big a project to tackle at this point, budget for it down the road and treat the problem. This is almost always heat tape, which is essentially an electric cable that warms up to melt a pathway for the water. They use electricity and must either be manually controlled or be attached to a sensor that can tell if there is both cold temperatures and moisture present (otherwise you're wasting a lot of electricity - potentially $15 or $20 a day if you have 100 feet or more).
While you can buy basic systems at home improvement stores, your best value is to have your roofing contractor install a system for you. He or she will know the proper placement, how much you need, and will work with a licensed electrician to wire it directly into your home's wiring system. Ideally heat tape is on its own dedicated electric circuit. If this isn't possible you can plug in to an exterior outlet, but make sure there are no (or very few) other devices drawing power from that circuit at the same time (especially if you still have knob & tube wiring). My favorite manufacturer is Pentair's Raychem.
The "This Old House" crew also discuss tuning up your snowblower and furnace. While it's easy to assume that your furnace will crank out heat all winter long, it is well worth the cost to have an HVAC technician do an annual tune up. And remember to replace your filters!