Magic Duels

Below is a White/Red Aggro deck that I have built, and have had very good results when farming hard AI for gold. Played correctly, and with a good starting draw, this deck can easily net you a win by turn 5 or 6.
Plus, it is built entirely of cards from the starter pack, so you can use this right away if you are just starting out. I will incude some replacements, which you can use at your discretion as your card collection expands.
The basic idea is to lay out low cost creatures very quickly, and buff them with aura/enchantments to dish out quick and heavy damage before your opponent can play their higher cost cards. While an early win is possible, this deck does very well going into the late game.
Once you learn the deck, you will be well on your way to fast, easy wins.

The Deck:
3x Elite Vanguard - 2/1 for 1 mana? Yes, please!
4x Suntail Hawk - 1/1 with flying for 1 mana. Early attack/defense
4x Kinsbaile Skirmisher - Cheap 2 mana, and buffs your other creatures.
4x Nimbus Wings - Only 2 mana for flying and +1/2. Formidable early damage.
4x Inferno Fist - Can buff damage +2 OR deal 2 damage instantly.
2x Reprisal - To take out any 4+ power beaters that your opponent might have.
4x Twinbolt - Instant 2 damage to 1 OR 1 damage to 2 targets. Take out early defense.
3x Skyhunter Skirmisher - Cheap 1/1 flyer with double strike. Great when buffed.
4x Heliod's Pilgrim - Cheap 1/2 defender. Let's you draw an aura/enchantment. Nice!
3x Flaring Flame-Kin - This early with Nimbus and Inferno Fist will SMASH your enemies!
3x Juggernaut - Most expensive card at 4 mana. 5/3 that HAS to attack. Pressure up!
12x Plains
8x Mountains
2x Clifftop Retreat

Possible Replacements
Replace your small creatures(Elite Vanguard, Suntail Hawk, Kinsbaile Skirmisher) with better ones:
Anointer of Champions
Topan Freeblade - 2 mana 2/2 with vigilence and renown. Great early attack/defender.
Consul's Lieutenant - 2/2 for 2 mana with first strike, renown, and +1/+1 buff ability.
Iroa's Champion - 2/2 with double-strike for 3 mana. Powerful when buffed.

Perilous Myr and Goblin Arsonist are great replacements for the Suntail Hawk. Equal damage and toughness as the Suntail Hawk, but can deal 1, or 2 damage respectively, directly to an target creature or opponent upon upon death. Excellent for killing off those early enemy blockers, or dealing those last few points of damage to your opponents face to win the round. Always an annoyance for the enemy, those two.

Possible replacements for Juggernaut:
Kytheon's Irregulars - 4/3 for 4 mana with renown, and tap creature ability.
Archangel of Tithes - 4 mana 3/5 flyer that makes opponent pay mana to attack/block.
Patron of the Valiant - 4 mana 4/4 with flying, buffs already buffed creatures.

I really like Archangel of Tithes. It can leave an opponent severely damaged, or dead, if they spent all their mana during their turn and have none left over to pay for blockers.
Just that tiny bit of control over the battlefield can be the different between victory and defeat.

This isn't so much a solution, but an addition. The achievement pops after the match is over and saved. As of the Eldritch moon update, they still haven't fixed the in game tracker for the solo wins. Sadly this goes up every time you restart a duel. But since the match isnt completed, the win counter goes up, but you only get one win when it's saved and you finish tge match. You could have restarted the match 4 times, and it would show 4 more wins, but only save and count the one actual win. So if you are losing, just concede, or let the AI beat you. Hopefully they fix this soon.