Hot cocoa and how you like it is all about taste in my opinion. Some people like it very rich and chocolaty, and others like it not as rich.
So roughly add the following to your taste, you can easily vary any of the ingredients. I suggest put some together, try a little taste it, and modify it if it doesn’t fit your liking the first time.
Hot Cocoa Mix:
2 cups powdered milk
1 cup non dairy creamer
1/2 cup cocoa
1 1/2 cups sugar
Mix together in a small bowl. Serve by adding hot water and mixing well. (3-4 spoonfuls per mug is about right)