As we near the end of January, it is a good time to remind folks that tree maintenance on your deciduous trees generally is best done at this time of year.
With the leaves gone, it is easiest to view problems in the canopy. This can mean damaged and broken limbs that need removed. It also can mean removing healthy limbs that are rubbing other limbs or growing in a direction that will cause the form of the tree to become misshapen over time.
Let's first give your mature trees a good looking over. With exposed branches you can see if the past year's storms have caused any damage. It's best to prune damaged branches back to the nearest main fork or even the trunk. Pruning allows the resulting open wound to dry out so that it's a less attractive entry point for insects or fungal diseases in the spring. Trees naturally create a hardened barrier in the wood directly under an injury that is more resistant to insects and disease. Trees repair wounds by covering them with new wood called callous tissue. The more rapidly this forms to cover the wound, the better. Wound dressing paint is no longer recommended to cover pruning cuts since it can interfere with a tree's normal healing process
Now for the young trees. Like children, these young trees often need "training" if they're to grow tall and straight. I planted an oak in my yard a couple of years ago and it's developed a side branch near the top that is way too long. It has become the main lead in what ought to be a straight trunk. A shorter, but straighter, branch should be the main lead, but too much energy is going into the wayward branch. I could just cut off that branch, but the little oak needs as much leaf surface as possible next year to gather sunlight. Instead, I'll just prune off the outer end enough to allow the desired straighter branch to become the future trunk. Virtually all of the existing side branches on this young oak will eventually be pruned off as the tree grows taller. Some side branches, as yet unformed, will eventually become the main first branches of the tree. Work done now will help to insure that the young tree matures with good shape and strong branch structure.
With both young and old trees, other things to look for include weak forks where the angle between two branches is too narrow. Bark is often trapped in the fork as the two side-by-side branches grow larger. This leads to a weak connection that is likely to break during some future wind or ice storm. Breaks like this often tear a lot of bark and leave a big wound that is slow to heal. Broken weak forks can even wreck the whole crown of a tree if not caught and corrected soon enough. Branches that grow inward within a tree's crown or crossed branches may lead to future problems, too. They can interfere with the growth of other branches or lead to worn bark when two branches constantly rub each other. Injured bark is a likely access point for disease and insects. The sooner that any of these conditions are recognized and addressed the easier it is to accomplish.
You can do much of the necessary work yourself on younger trees with only a small investment in some simple tools. You may need the help of a qualified tree service to do higher work, though. They're trained and equipped to do that kind of work safely. It'll cost you something, but the investment in your trees is worth it. Your trees will pay you back many times over.