It's all about the testing

This is Shikamaru Pwns Anyone, or Jeremy. I am from Minnesota and I consistently play with Mr. Veazie. My accomplishments include winning MN’s Jonin (now SJC) in 2009 and topping Gencon that same year. Since then I have been on the bubble and have given the win to teammates and friends. My favorite things about this game as of now have to do with the deck:  the versatility in deck construction, and building the decks rather than piloting them.
How to prepare for an event:
Most players will just pick up their deck and play the next day. Or playtest hands by themselves because they either don’t want to share their deck, or they have confidence that they will be able to win without testing at all. I can say from personal experience that this is not the best way to approach an event.  Testing needs to occur in order to build your deck and have the utmost confidence in your deck.
The first thing you need to be able to do is have versatility in your testing. That means having decks X,Y and Z and mixes between all of them. You want to have a good idea of what you will be playing and know how your deck will react to the meta. Whenever I test for an event I always try and have the decks that I will be testing against built even if they are not the prime versions (ie having a mill deck built). If your deck is struggling against a certain type like mill or rush, than you will have to do one of the following: change your deck, change minor things in your deck, or change things in your sidedeck.
You also need to make the small changes while playtesting to prepare for an event .You play though your deck (even if it is just drawing hands by yourself) to see what flaws you have made in deck building. Some players choose to play with lower ninjas and more mission and jutsu. For example, some players will play the standard 10 zero turns. And others will go down to 9 or go up to 11. I personally always go up to 11. But these are important decisions that could make or break your deck by missing important drops in the early game.
Know what you will be playing against, both decks and cards. Staple cards and the most powerful cards in the game are different. Your deck has to be able to either counter these cards or counter back with your powerful jutsu’s. Realize that in the current meta, fourth hokage, rasengan, and fireball could come at you at any point. Your deck needs to have specific answers for these cards or it will be harder for you to answer them.
Two other important qualities in preparing for your event are to know the top players and to know the type of players you will be playing against. By knowing the top players you can usually guess who will be at events by the Bandai boards and their current area. Knowing who you will be playing against can help you with both your deck choice and how you approach to play against them. You may have to play more conservative against some and rush more against others. By the type of players I mean that going to specific areas you can usually judge what kind of decks will be more prevalent.
And last, but certainly not least, just play. You should test your deck as much as you can before an event to both feel confident in yourself and also your deck. Good luck and happy testing.