Make sure the pan that you're using has a tight fitting lid and handles on both sides so that it's easy to lift and hold. You'll be shaking the pan during popping, so use oven mitts or pot holders to protect your hands from burns.
Heat the oil in a large saucepan or pot over medium heat. Add the butter and allow it to melt.
Add the popcorn, then evenly sprinkle the sugar and cinnamon over the un-popped kernels. Place the lid on the pot and increase the heat to medium high.
When the corn begins to pop, use the pot holders or oven mitts to hold the lid firmly on top of the pot. Holding the pot by the handles, carefully remove the pot from the heat and shake it up and down a few times. Return the pan to the heat and allow the kernels to continue popping. Shake again every 30 seconds or so to prevent the popcorn from burning.
When the popping slows down, turn off the heat and carefully remove the lid slightly to release some of the steam. To avoid being burned with steam, lift the lid away from yourself. When the popping stops completely, remove the lid and sprinkle the popcorn with 1/2 teaspoon of salt. Empty the contents of the pot into a large bowl and finish salting, to taste. The sugar will be very hot, so toss with a wooden spoon to prevent your fingers from burns.
Resist the urge to throw your face into the bowl and enjoy.