Heads on coin
Press A exactly when Pikachu's face is showing.

Tails on coin
Press Up right before the coin is displayed.

See your deck
Use a card to see your deck. When you see everything, turn on the game and select to continue the duel. The cards will not be shuffled and you know what's coming up.

Trainer in disguise
The person in green in the Psychic Card Club is your character in Red, Blue and Yellow games.

Walking Faster
Holding the B button down will allow you to walk faster.

Fast Card Shuffling
Pressing B will let you fast shuffle the cards fast.