Do you ever have your characters in costumes? Whether you are writing about a modern character going to a Halloween party, or writing about a bunch of people living in an era or location where the clothing is different from what you wear everyday it can be very important to describe it accurately. Make sure that what you see in your mind is being related on the page.
You can get a lot of practice from the fact that Halloween is coming soon and most of your family will be wearing costumes. You can describe costumes and events like Halloween parties, haunted houses, and other festivities and decorations on a blog, in a journal, or even writing a short story to get some experience writing about costumes. Makes sure you don't use pictures: that's cheating.