Always shout "HEART OF THE CARDS!" before drawing any card.
Add Shapesnatch to all your decks. You can summon him from your deck on turn 1, declare victory and leave. At the very least your opponent will feel defeated.
Always start a duel with a hearty "gl hf" and end it with a "gg". Good manners is what makes people want to continue losing to your awesomeness.
Learn about card advantage and what it can do for you. Then use that knowledge when making decks.
Learn about the most popular decks and think "how does the deck I'm making have ways to deal with those decks?"
Have fun, don't get upset when you lose, don't ragequit, don't be a bad winner, and most of all remember that this is a children's card game and your pride as a duelist is not anywhere near the level of your pride as a person - so don't take things too seriously. If a noob won't admit a mistake, just laugh at him/her and leave. Don't have a heart attack over it.