I've played this deck in MTG Arena to get to Mythic each season.  It's easy to use, and strategic, so you get a real feeling of acomplisment every time you win with it. Here is the general how to;

• The Mainboard is the deck if played as Bo1. The sideboard is if you decide to play it in Bo3. I found the deck wins more often in Bo1.
• Don't be scared to muligan till you have at least 3 land in your hand or 2 land and a Llanowar Elves (if you can cast it with the mana in your hand on turn 1 or 2).
• The first goal every game you have is to ramp to 4+ mana with Llanowar Elves, and Dragon's Hoard. It's better to not play a Dragon Egg, play Dragon's Hoard, take damage next turn, then on your following turn to play a Demanding Dragon on turn 4.
• Don't be scared to take damage, or your planeswalkers take damage. If it's not gonna kill you, it's safer to preserve your resources.
• Don't be scared to sacrifice Llanowar Elves to Fiery Cannonade in the mid to late game. Once you have 5 land you can summon at least 1 Dragon per turn.
• Be creative with mana ramp, and spending mana. You can tap Dragon's Hoard the same turn you play it to cast a Llanowar Elves, or another spell, and you can use Sarkhan, Fireblood +1 ability to get 2 mana of any color to help cast a Dragon.
• You want Dragon Egg to be destroyed or sacrificed. Use it to block, anything, sacrifice him as a result of one of your opponents spells. Cast Fiery Cannonade to kill it. When Dragon Egg dies you get a 2/2 Flying Dragon creature token with "(R): This creature gets +1/+0 until end of turn.". That gets devestating, and you can activate it after the opponent decides it's blockers making it a great kamikaze creature to destroy a strong creature or planeswalker an opponent controls.  You will also find even in Mythic - players tend to not even realize this small dragon's powerful ability, so use it to outsmart the enemy.
• Lathliss, Dragon Queen should always be played before any other dragon in your hand - when possible. With this creature on the field it creates a 5/5 Dragon with flying any time you have a Dragon enter the battlfield. This includes when you play Dragon Egg.
• You want to be stomping. Each turn you want to attack with dragons if you can. Even if you lose one. This deck is built to keep droping 1-2 Dragons each turn and keep attacking till the enemy destroys them. Obviously you wouldn't swing a 5/5 Flying Dragon into the 6/6 Flying Spirit without having Spit Fire, or Fiery Cannonade to destroy the opponents creature after.
• Sarkhan, Dragonsoul's only goal is to actiave that +9 ability. It only takes 2 turns for him to go from 5 Loyalty counters to 9, and completely worth destroying him spending 9 counters to play. Every. Dragon. In. Your. Deck.  Used with Lathliss on the field, or through the use of this ability summons a 5/5 Dragon Flying token for each dragon you summon.
• Demanding Dragon is in my opinion your most powerful dragon in your deck. Forcing your enemy to take 5 damage, or sacrifice a creatue. While being a 5/5 Flying. Can defeat your opponent playing all 4 of them if they are not paying attention, or defeating your opponent when they choose not to sacrifice a creatue 3 turns after, or 4 if they did. Combined with the stomp from the rest of your deck that becomes a lot faster.
• Skarrgan Hellkite is great as a 4/4 haste, but if against a weenie deck. Perfect for clearing 1's and 2's. Combined with one or two Fiery Cannonades to take out added 3's, 4's, and 5's.
• Verix Bladewing is great as an early way to get a Dragon out for 4 mana.  I tend to try and push it for it's kicker ability to enter the battlefield with another Dragon token. Just when you have 4 Mana, it seems more worth it to further mana ramp, clear opponents creatures, or summon another dragon as opposed to this, but in a game where you are having a slow game. Getting this out for it's 4 mana for a 4/4 flying can be a game changer as well.
• Dragon's Hoard is great for getting Mana ramp early, combined with Llanowar Elves, and Sarkhan, Fireblood.  Into the middle and late game, using this to draw more cards becomes most important.
• Fiery Cannonade is in the deck to clear the battlefield of low toughness creatures. Don't be afraid to use it against only one creature. Don't be afraid to kill Llanowar Elves, or Dragon Egg. You can cast 2 a turn for six mana and clear a field of 4's.
• Return to Nature The only reason green is in this deck is for Return to Nature and Llanowar Elves. Red doesn't have much in the lines of Artifact AND Enchantment removal and the current meta calls for Enchantment removal if you even want to be viable. You can certainly add one or two more of these to your deck as your choosing. I just found having 3 or more made them the only spell I could draw, costing me a lot of games on that alone. However if you are against a deck that relies heavily on it's Enchantments or Artifacts running 4 of these are perfect.
• Sarkhan's Unsealing I tend not to play unless I actually need it. In your turn when you can play a spell with 4 mana you tend to have just ramped up to 5 or 6 mana, and playing Lathliss, or Demanding is a lot better than playing Unsealing.  However I have found that when another stomping deck like the Green/Red Dinosaur deck, this card saved my life more times than I can count, so it remains in my deck as a failsafe.
• Spit Flame is an entirely underrated card. You don't need more than one, ever, and as the only one in your deck when it gets in your graveyard you have a point and destroy 4 damage any time you need it. Another failsafe.

The Sideboard and Deck Counters
• Jaya's Greeting came out with the release of War of the Spark. It's lightning bolt, but you get to scry. Scrying is helpful in this deck, for getting your Dragon's out faster.
• Rekindling Phoenix It just keeps coming back.  This creature is so hard to kill unless you exile it, and even then if you have a Naturalize more exile cards you get it right back when you destroy them.  If you are against a deck that relies on stomping this card can save your life, and it combo's excellently well with Sarkhan's Unsealing.
• Banefire is great when you go against midrange decks that get creatures to toughness levels that stacking Fiery Cannonade won't compete with. Enemies has a 12/12 creature. Attack with your Dragons, deal at least 4 damage to it when they block. Then Banefire that thing for 8 damage if you have the mana to spend for it. Combo it with Spit Fire, or Fiery Cannonade to deal even more damage.
• Fiery Cannonade sometimes you get against a weenie, and/or agrro deck. If it doesn't have enchantements drop Naturalize for another cannonade.  Having 4 Cannonades in your deck over 3 basically confirms you will get at least 1 or 2 every game, and this will decimate any agrro and/or weenie deck.
• Return to Nature it's in the ability of the card. If you are agasint an enemy with more artificats/enchantements in their deck. Like a deck based around exiling any creature you play. This card becomes essiential and dropping other spells for it will be game changing and turn the table in your favor.
• Rhythm of the Wild any deck that is running counter spells. This will save you every time.

The Maybeboard
• With Dragon's Hoard, and Sarkhan, Fireblood, you actually the ability to play Dragons with more than just Red or Green casting costs. If you are feeling lucky, switching 2 to 4 creatures from the Maybeboard can make this deck even more fun, unique, and feel more rewarding to play. For example, removing Verix Bladewing and a couple Skarrgan Hellkite for 2 Nicol Bolas, the Ravager // Nicol Bolas, the Arisen and 2 Niv-Mizzet, Parun benefitted the deck and made it more fun.
• I removed Lava Coil and moved it to the maybeboard.  I have stopped using it in the main deck, and was not touching it in my sideboard, so with the release of War of the Spark I have decided to remove it entirely. War of the Spark is going to spike many aggro decks, bestfriends decks, and decks mainly running planeswalker - so Lava Coil will become mute against those decks. However it still is a great removal card in my eyes, especially since it stops any effects that activate when their destroyed, sent to the graveyard, or effects from the graveyard from happening, so if you too like the card. Maybe put it in your deck in place of Jaya's Greeting
• You can run Nicol Bolas, Dragon-God and make a "Sarkhan the Mad" type deck if you add some black mana.
• Sarkhan the Masterless could be added to the deck if you are willing to sacrifice some ramp, clear, or Dragon's to put it in the deck.