This is kind of ridiculously simple, so I'm not sure it qualifies as a DIY... but it's a quick and inexpensive tip to make your home smell like autumn amazing-ness. Since it's officially October, I think the timing is perfect for some fall aroma around the house.
I was at the grocery store the other day and came across packages of mulling spices and cinnamon sticks, which reminded me of this easy method of home aromatherapy. I learned this trick from one of my college roommates...
