There is no more important aspect of performing a proper deadlift than creating tension. Tension through the core pillar ... and tension through the lats.
A weak core and inability to activate the lats through the full concentric and eccentric phases of a deadlift is the easiest way to sabotage your gains ... and worse, leave the door open to injury.
So, in addition to performing real core exercises that train the core pillar to brace and protect the spine, learning how to properly engage and activate the lats should be the top priority in your preparation for deadlifts and other foundational hip-hinge movements.
We often think of the lats as the muscles that span the side of your back from the armpit to the waist. Actually, their form and function are much broader. The lats connect the rear ribcage, upper arm, pelvis and hips. When properly engaged and activated, they blend these critical areas into a functioning unit.
It's a mistake to think that strong lats are going to improve your deadlift. In other words, that dude in the gym doing seated lat pulldowns with the whole stack isn't doing anything other than showing off. Latsturbating, if you will.
To learn and cue proper lat activation and tension that will transfer to heavy pulling, all you need is a resistance band and something around which to anchor it. It's example No. 7,876 of how people unnecessarily complicate their training when it really should be quite simple.
Check out this article from Dr. John Rusin to learn all about the straight-arm lat pulldown and all its variations. Then, incorporate these activation drills into your training -- especially before a heavy pulling session -- and let us know in the comments how it goes.