#1. Get cards not perma-banned, and that are good. Like Marina!
#2: SPEED IS YOUR FRIEND. If a battle takes too long, it could seriously hurt your score. A fast loss is better than a slow win.
#3 If you have no hope on winning, lose! Noobs always play in tournaments, so pick on them! (And bail the moment you see WMD Malachi. JUST. LOSE. FAST.)
#4: Be quick on your toes. The moment a battle's over, don;t even wait for your missions or just turn them off.
#5: and finally, remember to have a calculator!