Just take paste wax, like for floors, and wax all around the surfaces where the door meets the frame. Don’t use liquid wax, use the old-fashioned paste wax, sometimes sold as “bowling alley wax” in some of the bigger grocery stores. You have to wipe it on and then rub it a lot (like polishing a car) until it looks shiny. Do 2 coats, preferably, but follow the instructions on the can. The idea here is that the water will bead up and flow downward, by gravity, a lot better on wax than just paint or metal surfaces, which encourages it to drain better. Also, ice has a real hard time sticking to something really slick like polished wax. On one car I had, one treatment in the Fall lasted the whole winter, usually, but very rainy or snowy climates might need it more often. It took me about fifteen minutes, no big deal. If you get stuck with a “frozen” door and it’s not too far from the house or garage. a good way of getting it unstuck is using a hairdryer and an extension cord. Another hint is to get in another door, start the car, and let it run with the heater set as high as it will go. Either way will usually work, and both works faster. If it’s too cold then to put the paste wax on, you could just try a spray wax like Pledge on all the door-edge surfaces. Should help a lot, if not as well as the paste-wax treatment. While WD-40 will usually prevent freeze-ups, also, it can be very damaging to synthetic rubber products, causing them to crack and fail prematurely. No point in destroying all your door weatherstripping, in my opinion.