There are three dices whose faces have different numbers from one another faces. Therefore numbers from 1 to 18 are distributed on the all the faces of three dices.
Well, we prepare the following dices which have the configuration:
|Dice A||Dice B||Dice C|
Actually, the above dices have an intriguing feature as follows. If your friend choose the dice A, you can win by dice B with the probability 7/12. If your friend choose the dice B, you can win by dice C with the probability 7/12. If your friend choose the dice C, you can win by dice A with the probability 25/36.
Therefore, you can always earn the higher probability than your friend.