Using the Decoy Die
technique effectively comes down to showmanship/acting ability more than anything else. You have to remember that most experienced opponents will doubt you're actually making decisions based on rolling a die, particularly if you use it every throw, since they know you know that randomness is not conducive to excellence. So the ability to bluff them by acting the part convincingly is essential.
Here are a few other tips for Decoy Dicers:
(a) only roll for particular throws - for example if you only roll the die when you have just lost a throw, your opponent may be more inclined to believe you're using it for real, since this is a point when many players will rethink or shift strategies. Rolling it before the first throw may also be more convincing than at other points during the match
(b) only roll it when you've already decided you're going to repeat your previous throw - if the opponent believes you're using the die for real, he will assign 1/3 chance to you repeating the throw, whereas otherwise he may have assigned a higher chance to that possibility
(c) hide the die from your opponent, making it seem like you don't want them to see what you roll. Aside from making it more believable, your opponent may become frustrated, particularly if they're a nosey person who hates not knowing something, which may throw them off their game
(d) don't hide the die too well - if your opponent can see what number you roll sometimes, he will be trying to link the numbers to your throws, and the extra braincrunching involved may distract him and throw him off his game. Alternatively, you might roll the die completely openly, but use a different-sized die each time (you can purchase d4, d6, d8, d10, d12, d20 in most games shops), again causing your opponent to become confused and distracted as he tries to figure out your algorithm
(d) become a 'Dice Man
' - if you act according to the die before the tournament (for example, letting it determine what beer you order, or - for more advanced dicemen - what mood to be in when talking with another player), espouse the benefits of Dice Living, and in general appear to random, spontaneous and borderline crazy, then other players may be more inclined to believe you will play according to the die. The bonus with this is that dice living is an
insane and dangerous
interesting and creative way to live, so it's worth doing once in a while in and of itself, whether or not it helps your tournament chances.