This question came through on reditt:
The simple answer is to pull the slack out of the bar.
This is better explained in our free Deadlift Manual
Pull The Slack
The first thing to do after the setup is to pull the slack out of the bar. Reach down and grab a loaded barbell. Hear that clicking sound? That’s the sleeve of the barbell connecting with the collars. You want to remove that play before you initiate your pull. That’s what guys mean when they say to pull the slack out of the bar. Doing this initial “pre-pull” allows the hips to drop down slightly. Although this step is subtle, if skipped, the hips will slide out of position once you really start to pull, which is when the weights break from the floor.
Source: Deconstructing the Deadlift