Inspections should take place once a year, along with other heating appliances such as furnaces and stoves. Inspections are important in order to prevent problems from occurring in the future and fix any current problems your chimney and fireplace might have.
What should I look for when cleaning the chimney/fireplace?
You should clean your chimney and fireplace as necessary, but at least once a year is best. If you notice soot buildup of even less than half an inch, it means it's time to clean your fireplace. Any accumulation of soot can result in a chimney fire, so cleaning it out is very important.
What else should I know?
It's best to clean your fireplace and chimney before the winter and inspect it afterwards since you'll likely be using it more often during this season. It's important to remember that insects and birds often get in the chimney, making it their home, so you must check for and remove any debris or nests they leave behind.