Static electricity is caused by your body picking up free electrons as you walk on the rugs. When you have extra electrons on your body and you touch a metal conductor, such as a door handle, the electrons flow into the object and you get a tiny shock.
During the summer, the humidity in the air helps electrons flow off your body, so you don't build up a charge. The air is drier in the winter, no matter what type of heating system you have, allowing a larger charge to build. Humidity will certainly help reduce static electricity, so installing a whole-house humidifier is one option.
Another option is to treat your rugs with an anti-static chemical as shown. Spray-on treatments are available at many carpet retailers and online (search for “anti-static carpet treatment”). Carpet companies also have anti-static carpets available. Most residential carpets sold today have some sort of treatment applied at the factory.
A third option is to wear special shoes that dissipate static charge. The shoes have conductive strands in the soles that discharge static electricity as you walk. You can find the shoes at select shoe stores and online at sites. The cost is comparable to standard shoes.