A lot of it has to do with color. There are definitely colors that come to mind when we think of a particular season. Adding in or swapping things out for more seasonal colors instantly transforms your decor. I don't have a whole lot of "fall" decorations. I do have a few pumpkins and small things that say "Fall" or "Harvest", but other than that, I decorate with fall colors-oranges, browns, rust, gold, etc. Even small additions and changes can make a big difference.
Also, purchasing some small pumpkins and gourds is an easy way to decorate your home this time of year.
What about you? Has fall arrived at your house yet?