An ounce of prevention is worth a pound of cure...this old adage most certainly holds true when it comes to rust and your car. Rust isn't just unsightly, it is actually harmful. Because the body of your vehicle is what shelters its inner workings and components, when the exterior becomes compromised, the “innards” are then threatened. A given car may be perfectly capable of lasting up to nearly 500,000 kilometers of use, and yet be forced into retirement far earlier than that simply owing to rust damage.
In order to prevent rust from finding a home on your vehicle, you should regularly maintain its body. Washing is important, since dirt compromises the body. When washing your vehicle, you should ensure that you don't just pay attention to the parts that are obvious, but also to the undersides and crevices, where salt is most likely to settle in and begin its nasty work of corrosion. Using small brushes will help you to access small, awkward spaces. Be sure to rinse off any cleaner that you use very well (and try to use a gentle one to begin with). After this has been done, be very diligent about drying...excess moisture is, after all, a key ingredient in the production of rust.
If you find that, despite your best efforts at rust prevention, a spot still manages to creep up on your car, the sooner you remove it, the less damage will occur. When removing rust, you should always ensure that you are wearing safety gear: gloves, mask, and protective eyewear are good basics for this. Protecting your car from the work you are about to do is a good idea as well: since you will be spot treating, you don't want the whole car exposed to the mess that may ensue. To prevent dust and debris from traveling to nearby nooks and crannies, seal them off. This will limit those particles' abilities to find new homes to damage elsewhere on your car. Additionally, you should seal off the entire underside of your car using tape and good, thick paper.
The technique you use for removing rust will depend upon how deep the damage actually runs. If it is quite close to the surface, then abrasive techniques will do. You could use sandpaper that you rub the area with manually, or you could use an electronic sander. Either way, you'll want to sand down until you see unpainted metal, ensuring that the entire portion of rust has been removed. Once this is done, clean away the dust and debris very well, apply primer, paint, and a top coat. If, after sanding down to the metal, you find that the rust has actually worked its way into the body of the car leaving pitting (but not actual holes), you'll need to scrape out the damaged portion with a wire brush. Once you have done this, sand the area to a smooth finish, and continue with the steps of cleaning, priming, painting, and finishing as before. If, after sanding down to the metal, you find that trust has made a hole in the body of the car, it's time to seek a professional's expertise. Unfortunately, this type of damage cannot be handled at home, and you'll need an expert to tell you whether it is reparable or not.
Long winters, like Albertan winters, can take their toll on vehicles if we aren't diligent about preventing rust and corrosion. The good news, however, is that the preventative measures we take for this are surprisingly simple: regular cleaning, and wiping of excess moisture. Regularity with these practices should limit the amount of rust you see on your car a great deal.