You should be having your chimney cleaned and inspected on an annual basis. If you don't have this done, then you can end up dealing with a lot of problems that could have easily been prevented. Here is more information on chimney inspections and cleanings.
Know the best time of the year for you to have your chimney tended to
You may want to decide to have your chimney taken care of at a different time of the year than some of your neighbors. This is because your situation may differ from theirs.
If you haven't had your chimney cleaned in a while and you plan on using it in the upcoming winter months, then you should have it tended to in the fall. Your chimney will have a buildup of creosote, which is flammable, and you will want it cleaned out before you use the fireplace.
If you or someone in your house has allergies, then you might want to have someone come out to clean your chimney in the spring. When you use something in the home that removes the air, like an exhaust fan, then that air gets replaced by way of the chimney, and this is how allergens come into the home. By cleaning the chimney after you are done using it for the winter, you will reduce the allergens and make sure the fireplace will be fine to use the next winter.
Have your chimney cleaned even if you don't use the fireplace
Don't make the mistake of thinking the chimney doesn't need to be cleaned because you don't use the fireplace. Chimneys are common places for bees, birds, and other wildlife to use to build their hives or nests. Sometimes, these nests can be huge, and they can lead to damage to the chimney. Plus, if you did decide to light a fire one day, the nests are flammable and can cause a chimney fire. By having the chimney inspected and cleaned, you will ensure that these types of problems are ones you don't have to worry about.
You want to take all possible measures to ensure that your home is safe, comfortable, and free from allergens. An easy way to for you to do something that helps achieve these things is to call a chimney cleaning service and ask them to come out to inspect the chimney and then to clean it for you.