I just returned from a fantastic trip to Yellowstone in winter. Lucky for us we had a clear morning with ice on the trees, and lots of frosty wildlife. A lot of the wildlife was moving slow, so you could really set up your shot. Bison just seem to wander down the trail in winter, and coyotes often pause to watch the snow coaches go past. We even had a good sighting of wolves, but a little far for my 300mm lens.
One point I often make in workshops is getting eye level with your subject. Photographing from six feet up on a tripod is easy to do, but may not result in the best image. If you can (bad back and knees can prevent this!), try a lower position like on your knees or even lying on the ground. Lying in the snow in subzero temperatures might not be what everyone wants to do, but take a look at your images shot at tripod level and those at ground level. You feel more connected to your subject when you are at its level, and many times the background will be more interesting. If I had photographed this coyote at tripod level, he would have been against all snow. By lying on the ground, he was positioned against a dark background creating more separation, and we feel more of a connection being at his level. This image was shot wide open at F4 to further separate the coyote from the background.