Add the sugar and cinnamon to a small bowl. You can use between 2 tsp - 1 tbsp of cinnamon, it depends on how much you like cinnamon! I used the full 1 tbsp.
Stir together until evenly distributed. Spread out on a small plate.
To rim the glass, dip the whole rim (or just a section) in water or simple syrup held in a shallow container (big enough for the glass to fit).
Dip the wet rim into the sugar mixture.
Set aside to dry while you make your cocktail.
Notes
The nutrition info is off as it's taking the full amount of cinnamon and sugar into consideration. Variations
Mix up the spices - cinnamon is not the only warming fall spice that will work here: ginger is a great addition as well as a small pinch of nutmeg, cloves or cardamom. But only a pinch as they can be quite overwhelming! Pumpkin spice mix would also be great for pumpkin drinks.
Add a touch of salt - cinnamon works best in a sweet rim, but if you're making a holiday drink such as my Pumpkin Spice Margarita where a salted rim would not be out of place add a little salt for a sweet 'n' salty rim situation.
Citrus - Fall flavors go really well with orange! You can zest some orange peel and mix that in with the cinnamon and sugar. It will be a little heavier and may not stick as well, but the nice aroma you'll get as you bring the glass to your lips will be heavenly.
If using simple syrup, I like to dab the dipped rim super lightly on a paper towel to catch any excess so it doesn't drip down the side of the glass.