From a post in another forum, somebody mentioned that they would bring to the attention of a Team's head coach that he/his crew have noticed something while watching video of a/some of that team's previous game(s) that is/may be illegal. Wow. Don't EVER do that. That is a recipe for disaster. That coach/team will now believe that you are out to get them, and nothing you say will convince them otherwise. You will have h-e-double L the entire night, and possibly have a formal complaint lodged against you. And, if your state allows teams to 'scratch' officials, you can bet you will be scratched by that coach, wherever he may be coaching.
OK, so you see something in video that is a foul, should have been called by previous crews but hasn't been, and you want to use preventive officiating to stop this before it becomes a problem during the game. As it should be. The thing to do is observe the team - as you should always do during pre-game - and, when/if they show that potentially illegal action, THEN have the conversation with the coach about that action, and that it is illegal, and give him the reason(s) why. Don't threaten, i.e., "If you don't stop doing that, we'll have to flag you." Rather, just tell him, "Coach, we just noticed that tailback #11 tends to lean forward before the ball is snapped. As a back, he may be moving backward or laterally, at the snap, but, he can't be moving forward, and, if you also have a motion man, that will be an illegal shift, regardless of which direction he is moving." Hopefully, he will get that corrected. If not, then make the call during the game. To paraphrase the two Bobs from Office Space, that should "...fix the glitch."
Some things are harder to prevent. Maybe you notice in video that their slot backs are actually on the line, or they 'pick' a lot, or have ineligibles downfield a lot, or illegally 'stem' a lot. Those things may not show up during pre-game. For those kinds of things, try to issue warnings the first time they happen during the game (to the player and the head coach), and then make the call if they don't adjust accordingly thereafter.