Is there a ratio between these ingredients which comes out tasty?
-FrL-
You might want to look up Mexican hot chocolate recipes.
Try the recipe on the side of the Hershey’s cocoa box, but add some cinnamon. Or some Hot Damn.
About 8-12 oz milk, 1 tsp. cocoa powder, 2 tsp. sugar (cocoa powder is bitter), cinnamon to taste (1/4-3/4 tsp. range), and a pinch of salt to balance out the flavors. Heat slowly on a stovetop in a pan to get the ingredients to blend better.
This is, more or less, an estimation of what I do when I make cocoa/hot chocolate on the stovetop.
There’s no recipe I can find on the box. That’s where I looked first. 
-FrL-