Tree trimming, when done properly, should help your tree stay vibrant and alive. If your tree starts looking a bit worse for wear after you trim it -- for example, if the leaves seem to start withering and the branches start to droop -- then you're likely making a mistake or two in the way you go about trimming. Here's a look at three tree trimming mistakes that may be harming your tree, and how you can avoid them.

Mistake #1: Trimming away newer branches, rather than older ones.

A lot of people who are inexperienced with trimming trees assume they should just trim out any branch that looks too long or out of place. However, this can be a mistake if the branches you end up trimming are the newer ones. Once you remove those, all that's left is the older branches -- and without any new growth to capture sunlight and manufacture food, the tree may start to die back.

When trimming, make sure you are removing primarily the older branches. These are the ones that are darker in color. Their exterior will be brown and scaly, whereas the newer branches will still be at least partially green. Leave most of the new growth in place, only trimming away a little bit of it at the end if needed to shape the tree.

Mistake #2: Trimming too late in the season.

When you trim away a tree branch, the tree needs a little time to "seal off" the area where that branch once attached. If the cold weather arrives before this occurs, the low temperatures may cause damage to the tree and cause it to die back. Make sure you're trimming your trees in the early fall, so they have time to harden off before the temperature drops. Alternatively, you can trim them in the early spring before the buds begin to appear.

Mistake #3: Trimming away too many branches.

If a tree does not have enough branches left for its size, it won't be able to produce enough food to support itself. Experts recommend removing only about 1/3 of a tree's growth each time you trim. Remove more than this, and your tree probably won't do well. If you're not seeking to reshape the tree and only to keep it healthy, removing only the old, suffering branches, even if they comprise less than 1/3 of the tree, is even better.

Tree trimming, when done properly, should revive your tree, not leave it looking shabby. If you're not confident tackling this task on your own, consider hiring a professional. Many offer reasonable rates for a basic, occasional trimming, which is all most trees need.