Lots of DP
Go into the wireless connection and then go to leaderboard
(Note)this will only work if you have a DS wireless connection then there should be a duelist named Shawn at the top download him and duel him he is so easy he doesn't play any cards and for the best part once you win you get 150000 DP.
My Favorite Deck
I think the lightsworm deck is the best deck.
Dark Magician: beat the game, then find the duelist wearing the outfit in the Duel Runner shop. Either one will do. Beat them 10 times.