Agreed.
I'm actually very communicative verbally with the players but only to further aid that communication process when necessary. For instance, in response to appeals for fouls (which I'm not giving) or say, for an appeal that the ball has gone out of play when there's no flag, and I don't believe that it has.
In these cases, shouting something like "No, that's okay - that's a good challenge" or "Keep going gentlemen - play on please" respectively, helps with the flow of the game and aids your match control. Consistantly warning players prior to tackles/challenges however as alluded to by
@Lefelee is not something I'll indulge in. A player can play the "victim" card the minute you warn him. If he wants to make a stupid tackle that might cost him a card that's his business.