"You run to set up the pass."
That has become a football cliche. You frequently hear announcers and other analysts say it.
Running effectively makes it easier to pass. A team that can run it frequently forces the other team to move its safeties up to play the run, exposing the deep part of the field in the passing game. Going to play action can make defenses charge hard expecting the run and leave big parts of the field open. It can also be tougher for defenses to get exotic. Defenses have a tougher time mixing personnel, namely putting in extra defensive backs to create confusion because they are less adept at playing the run. They also cannot be as creative with stunts and other movements on the defensive front because it might leave a gap exposed right as the back is hitting it.
This is certainly one approach teams take, but there is no rule it has to be the only one. Teams can also pass to set up the run. It has pretty much the opposite effect. A lot of throws early in the game also impact how the defense approaches its task. A heavy passing attack keeps safeties deep, leaving running room open. If the offense utilizes a lot of formations with extra receivers, the defense will put in extra defensive backs who aren't as good at playing the run.
Teams can also take a balanced approach, keeping the defense guessing. Sometimes a balanced approach is rooted in building a gameplan around a defense's weakness.
I took a look at approaches teams take. When we are talking about establishing either the run or the pass, we are talking about early in the game so using Pro Football Reference's play index, I looked at each team's run-pass ratio in the first quarter of games this season.
Despite the old saying about running to set up the pass, most of the teams do the opposite. In fact, the teams that run to set up the pass are the exception.
The Jets were around the middle and tended to be balanced, throwing 53.58852% of the time in the first quarter.
Teams that pass to set up the run (Throw over 55% of the time): 18
Balanced (Both run and pass between 45% and 55% of the time): 12
Teams that run to set up the pass (Run over 55% of the time): 2