A few months ago I saw this recipe on Velvet Bird and have been loving it ever since. This is the yummiest and easiest way to make cold brew. The key is using good beans (I used Stumptown, one of my favorites!) because you will definitely taste a difference.
2/3 cup of course ground coffee
3 cups cold water
3 tablespoons brown sugar
1 teaspoon cinnamon  
Place all ingredients in a jar and let sit covered overnight in the fridge.  The next day (or next six hours or so, if you're impatient like me), pour it into a french press or strainer. It has a really great warm cinnamon flavor, so it does not need much, or any, sweetener. 
(All recipe credit goes to The Velvet Bird)