We in these parts are seeing our typical midwinter thaw so I figure it might give me a chance to do some pruning. Winter is a good time to prune because you can easily see the branches because they don't have any leaves.
Most trees and shrubs can be pruned at this time of the year no problem but pruning spring-flowering plants such as forsythia and viburnums will cut off the flowers so you need to keep that in mind. I will go ahead and look for broken branches or branches that I don't want and cut them out anyway. You should avoid pruning maple, birch and walnut trees because they will bleed sap when they leaf out in the spring. Although harmless, it can be unsightly and messy. These trees should be pruned in the fall but I've done it this time of year and it seemed to work out ok.
Pruning is something that should be done on a regular basis to keep your trees and shrubs in control and healthy. Most of the large tall trees like an oak should be done by a professional ISA (International Society of Arboriculture) arborist. Smaller trees can be done from the ground by using a combination telescoping pole saw and pruner. I've got one and they work great. The best is the style that has the small electric chain saw on the end. That's the way to go for the guys who have a lot to do.
What you are looking for are limbs that are damaged or look diseased. I also look for branches that are rubbing against one another, or cross, and those that are growing toward the middle of the tree or shrub. You also might be looking to reshape the plant or get it back under control. This is the time to do it because you can see the skeleton of the plant because it has no leaves to block your view. Pruning will make the shrub denser and give it that full-bodied look you might be looking for.
There is loads of information on pruning on the web and at the library or garden center that will help you make the right cut, but it's really not that big a deal, it's like art– you take your time and look at it from every angle and make the cut. What's nice is that mother nature will heal the wound by itself and recover well even if you cut a little to much. Don't sweat it, it will grow back and what you're left with is a healthier and better looking plant and, heck! It's winter and I'm outside gardening.