Swarming's Red Control

Mulligan for Flame Spitter, Underground Brigand, Groundshaker, and Flame Burst. Blood Singers, Seifer's Wrath, and Seifer, Blood Tyrant can also be worth keeping. Build towards both of your wells, and establish early collection as soon as possible.

Cap-10, Sky Pirate is good mid-late game for extending your deck, or when you just want some extra meat on the board.

Play your Devouring Plants preemptively, and deny your opponent's empty lands.

Try to maintain at least one Blood Singer on board, it's usually not worth it to have all three.

Don't play Hellfire when your opponent doesn't have any creatures on board, unless it secures you the win.

At the end of the day, efficiency with your removal i.e (1 dmg for 1 health creatures, 2 dmg for 2 health creatures, clearing 6 or 7 creatures with aoe) is what will win you games.

It should also be noted that at 3 legendaries and 10 epics this deck is fairly expensive to craft. These epics are central to the functionality of the deck. They are preferred to the cheaper removal options such as Firebomb, Blazing Salamander, Plague Bearer, Famine, and Punishment.

I realize that these tips are obvious to experienced players, and that this is a super common deck archetype, but after much trial and error this specific list has become my personal favorite. There is usually no shortage of collectors or of answers to your opponent's threats. Plus, Devouring Plant is a nice touch, if I do say so myself.