The day before, add 3/4 cups of ground (fresh if possible) coffee to a half gallon or similar sized jar. Add four cups of coffee and stir. Cover with plastic (mostly so the coffee smell doesn't completely take over the fridge) and place in fridge over night.
If you don't have simple syrup on hand, it is very easy to make. Combine in a sauce pan one cup of sugar with one one cup of water, bring to a simmer over medium heat, stirring occasionally, until the sugar is completely incorporated. Remove from heat and allow to cool to room temperature, before transferring to a jar for refrigerator storage.
Also, the day (or at least several hours) before cocktail hour, place the vodka in the freezer and the coffee liqueur in the fridge.
When the coffee has brewed for at least 12 hours, drain into another container. You can strain directly through a coffee filter, but I find it easier and faster to strain through a normal fine kitchen strainer first to get the larger grounds, then strain through the filter second. Returned the strained coffee to the fridge until ready to mix.
Chill the glasses you intend to serve the cocktails in.
When ready to serve, 8 cocktails is approximately 2 cups coffee, 1 cup vodka, 1/2 coffee liqueur, and 1/2 cup simple syrup. Mix together and serve in cold glasses.