It's fairly simple. The proper method in a dual is to announce the card before channeling your energy into it, activating it. The announcement is more for the sake of your opponent than anything, although there is an odd sort of exhilaration that can come from it.

The most important thing in designing a card is, to the best of your ability, cover your weak spots, but not so much as to make it impossible for an opponent to maneuver. It's more sporting that way. From there, it's up to the skill of your opponent.