I just find that telling players too much before a match, gives them more i bite on during the match. I.e, if you tell someone that you will book them for... , then you leave yourself open to ''you said you would...'' situations.
Well.. This season so far, I've had a chat with the teams in the changing rooms, and its very brief.. I tend to make them aware, that I will shout across the pitch at them, and that I have a zero-tolerance policy on the lip.
Needless to say, 2 games in and its worked a treat One person got a bit lippy, so I cautioned them, and they soon shut up. So, it does work, just not for everybody!
I always research the teams beforehand and talk to the managers about their season to date etc. For open age games I rarely talk to the players beforehand, just the captains at the coin toss - "lead your teams by example" etc. For youth games I generally talk to both teams separately, but keep it simple "no jewellry, play to the whistle, have a good game". I find that if you say too much about how you will referee then that gives you little flexibility during the match. They should all know the laws of the game by now.
I typically talk with teams seperately but not about what I expect from them in the game. I tell them 2 things...1) no jewellery of any kind, plase take it all off. 2) If you have any questions during the game, please ask me, but do it in a respectful manner and ask like a normal person would as a question. Other than that...have a good game.
These are things that would probably be told to the capitans during the coin toss however, that information usually never gets back to the teams so I much prefer to tell them myself.
Sometimes I'll say to the captains "you two are going to help me today with controlling your players, so thank you in advance for that. We'll both make mistakes, I won't shout at you for yours if you don't shout at me for mine", which normally gets a bit of banter going with the players like "don't worry ref, your mistakes can't be as bad as mine" etc.