These are the first cards I'd recommend removing to make room for upgrades: Compleation on a Budget Here's a list of $5 or less upgrade options for Breed Lethality to give you ideas on where to take the deck
Popular general enablers include cards like Enlightened Tutor, Mox Opal, and Elvish Mystic
After Eternal Weekend, I basically gave up
There are other tricks too, which well get onto in due course
#1 - Breath Weapon It's sort of funny to consider that a card to beat red is also a red card, but the power level of Breath Weapon against the Burn decks cannot be understated
Dont sleep on Author of Shadows, either sure its a ten mana combo, but exiling an opponents Teferis Protection or Heroic Intervention can help you close the game