For a stronger drink, use as many iced-coffee-cubes as you would regular ice cubes; for a mellower drink, use half of each type.
As the frozen coffee melts, it will blend into your beverage instead of diluting it, maintaining a kick that will stand up even to added milk or cream.
Just don’t freeze still-hot coffee (like the stuff you'd brew in your drip coffee maker) or use leftovers you’d otherwise dump down the drain. The bitter-tasting compounds in hot-brewed coffee will ultimately break down and turn sour even before they freeze, and nobody wants a sour summer. You also don’t want to use coffee cubes as the ice base for a flash-chilled brew, or your finished drink will be overpowering (and probably pretty bitter).
When a fancy mood strikes, mix cinnamon, a dash of vanilla, or chocolate syrup into the cubes for a DIY flavor boost. You can also use coffee ice cubes to blend into frozen cocktails, shakes, or smoothies, or crush them for a homemade granita, topped with fresh whipped cream. Drop a couple into a chilled glass with fizzy water and simple syrup for a spin on a coffee soda; experiment with tonic and homemade simple syrups. (Just be sure to clean the trays thoroughly before starting your next batch!)