B · Engine & Sequencing · §10
The order within a turn, and the one land decision that costs a spell later.
Within a turn the order is: land, the spell that costs mana, then the free spell, then attack, then any instant-speed pump after blockers.
Holding the pump until blockers are declared is free information. The only reason to cast it precombat is to reach the second spell for Flurry before the Monk can attack, which is a genuine trade and is usually worth it on the turn the Cutter lands.
A first draft of this guide told you to husband basic Mountains for . That was wrong, and a reader who plays the deck said so. is a land type: and are both Island Mountain, so seven of the eighteen lands pay that flashback and you will not run out. Fetch for colour and for the untapped source, and let the Dart look after itself.