The best time to get a Christmas tree? December 26! Stores are dying to get rid of their seasonal stuff to make way for the next holiday. Shop after Christmas for wrapping paper, bows, Christmas trees, and other decorations.
The same goes for Halloween costumes and decorations, Valentine’s Day candy and cards, etc.
This article from The Balance has a good list of when to get the best deals on certain seasonal items.
Apparently February is a good time to buy furniture and March can be good for air conditioners (given you don’t like in a hot state). I’m not sure exactly where they got this info from, but seems like a decent rule of thumb when looking for deals on certain items.