Now that you’ve tested your deck, pre-sideboard, post-sideboard and maybe even against itself (arguably a pretty important match up), what do you do with the information you have? You have to think of changes to make for your deck. Remember that list of key cards you should’ve made? These are the cards you should be looking at keeping – or making better by putting other cards that work well with these cards, like fetchlands for [card]Knight of the Reliquary[/card] or [card]Esper Charm[/card] for [card]Bloodbraid Elf[/card].
Too much of a good thing can be bad. If you have a lot of cards doing the same thing, they could hurt you in a different matchup. If you find yourself losing to a particular deck quite badly – think about why. It could be because you don’t have any flying creatures. It could also be because you don’t have a blocker – these things happen when your deck has too narrow a focus, and only wants to keep trouncing a particular type of deck, rather than the whole range of them.
Sometimes, you might have to trade a whole set of key cards for another, simply to give you a better chance against a particular deck – this could change your deck’s focus, or it might simply streamline your deck’s theme. Be sure to be mindful of this – I did this when I switched from Naya Ramp to Naya Zoo – and while they might share a similar mana base, the deck’s strategy, speed and methods changed entirely. This might not be to your liking.
It’s just as important to like the changes as it is to change your deck. Transforming your deck from simple Unearth + Discard strategy to a pure Unearth combo strategy could easily turn it from mediocre to awesome – but if you don’t like how a pure Unearth combo strategy plays – there’s really no point. The point to playing Magic is to have fun. If you can’t win with it, have fun with it.
There’s really nothing quite as exciting as pulling off that [card]Luminarch Ascension[/card] – over say, simply attacking with small white creatures. It’s rewarding to make your own strategy work rather than use someone else’s tried and tested crazy token deck instead of building your own token producing engine. It’s also fun to watch your opponent’s get a sense of foreboding as your innocuous looking [card]Khalni Heart Expedition[/card] gets ready to chop his life count via [card]Valakut, the Molten Pinnacle[/card].
Sometimes your deck just doesn’t work out – it doesn’t matter how much testing you do, how much tuning you do – you just keep losing. Don't keep working at it – try a new deck. Sometimes the deck simply doesn't suit your play style, and sometimes it just simply doesn't work. Some decks sound like awesome ideas – but they have some vulnerability only a larger card pool could fix. When rotation came along, the deck may have lost only a few important cards – but sometimes that's enough to take it from the top to being just mediocre.
A note – if you recall, many years ago I talked about why you might want to play 61 cards. However, fetchlands provide many of the advantages of playing 61 cards – while allowing you to play a 60 card deck. Fetchlands easily provide that half-a-land effect needed for that just-right land ratio – they also thin your deck of lands for the latter half of the game – so there’s really no good reason to play 61 cards currently. So don’t. (If you’re poor like me, play Panoramas and [card]Terramorphic Expanse[/card]s – unless your deck absolutely needs to have less
comes into play tapped enter the battlefield tapped lands)
The most important thing to learn from testing is how to play your deck. There’s nothing more embarrassing like playing TEPS and not knowing how to pull off the turn 1 win.