In a cup add 4 oz of Cranberry juice, squeeze 1 tsp of lime juice in the cup. Add some ice. Then fill the remainder of the cup ( about another 4oz) with your choice of sparkling water or soda.
I have tried it both ways, and know that people rather drink it with soda. If you decide to use sparkling water, the ratio is a little different. You don't want to water down the juice too much. Instead use 6 oz of Cranberry juice and 2 oz of Sparkling water.