When you begin a duel, pick either heads or tails, then while the coin flips, push A when it gets to your choice. As in , Heads; Push A when it turns to heads. It will work 95% of the time.
(I think it's easier when you pick heads)
On your first few turns of a duel send out creatures with a high amount of Mana and put it into your mana zone. (Preferably 5 or higher) When you have at least 6 cards in your mana zone put your smaller creatures in the mana zone. (5 or less mana) This way at the beginning you will be able to put out your small creatures and further into the duel you can put out big creatures safely.*
*This cheat does work. Tested by me and I won every duel so far and not lost a single one since I started!
Highlight the "Dragon Impase" card and hold select, L, L, R. And it should pop up and replace the card.