I used to write up my preseason packet, let the administration review it, then hand it out to the kids. The last page was a statement that said that the entire packet had been read by BOTH the athlete and parents and had to be signed by both before they can begin practice. This way, you have a paper trail that says both the athletes and parents have read and understand the rules. Then I turn those in to the A.D.
Then, very simply, we enforce those rules. First-year freshman or senior that's the a three-time State champ, it doesn't matter; everyone is the same. I had a senior one year, just missed going to State the year before, massive attitude problem. Had an unexcused practice the first week, and my policy was if you do that, you miss the next meet. When I told him he wouldn't wrestle the season opener, he shot back with some R-rated comments, talking about how important he was to the team, etc., and I tossed him off the team on the spot.
The rest of the kids were shocked, but most of them were glad to get rid of him. And, I didn't have another kid have an unexcused practice, or pop-off at me swearing.
Set your rules, make sure they're understood and don't waiver from them.