Here is a general deck building guide to help new players get started building decks in Magic Duels.
I don't recommend using the deck wizard in the game. It simply
gives bad card choices in some cases, and you can't go
back to edit those cards out.
It is ok for finding out some general archetypes in the game. For example, the blue white deck Control the Sky shows you that you can build a good blue white flyers deck. Just build it manually after.
A Magic Duels deck must contain between 60-100 cards. Stick
to 60 cards always.
Using the minimum number of cards increases consistency of the deck and adding too many cards decreases the odds of drawing your good cards.
A typical deck has around 24 creatures, 12
enchantments/instants/sorcery cards and 24 lands. Don't cram too many high cost
creatures with a converted mana cost (CMC) of 5 or
higher, stick to 2 or 3.
You may never get to cast them and you will be stuck with a handful of cards that you don't have mana for. Stick with the majority of cards in the 2, 3 and 4 CMC range.
It's not a bad idea to include some 1 CMC cards as well. Stick to only a few if possible, they lack power later in the game, but are great early.
You want about 40% land cards in your deck. So, for a 60
card deck you want 24 lands. Some decks can run more or less, but for now stick
to 24 lands.
A good way to calculate how many of each color land to add is to count the mana symbols on the cards. If you count 20 blue and 10 white you want a 2 to 1 blue/white ratio of lands, so roughly 16 blue land and 8 white.
The easiest way to grind gold is fighting the computer on
hard with an aggressive (aggro) deck.
The idea with aggro style decks is to overwhelm your opponent early with small low cost creatures, pump spells (spells that increase the cards power) and burn spells (spells that attack the creature or player).
Try to get the opponent's life down fast and use a burn spell to finish him off. Burn spells can also remove creatures in the way. You should be attacking every turn if possible when playing an aggro deck.
Here is an aggro deck I threw together using the starter cards:
Here is a good guide on www.untappedpotential.com for new players who only have starter cards:
I have also added the Lee's decks into Magic Duels Helper here.
Here is a comprehensive deck building guide written by LegendVD check it out it goes into way more detail:
If you are a new player and havent unlocked many cards check out new player deck list. I have added a few starter decks and some Origins only decks. Also check out OriginMD's Deckbox, which has a number of starter decks with YouTube guides.
In addition, you can now search for decks containing specific sets on the decklist screen. You may want to check the archives for older decks from previous seasons.