Just make sure that the pilot WANTS to be coached. Some do, some don't. I dont mind subtle comments about getting too close on the box ends and stuff.

AND make sure that you bring the right call sheet with you.
I was calling for Don Ramsey a month or so ago and accidentally brought the advanced call sheet to the line for a Masters pilot. Fortunatly I knew the Masters pattern so I was able to handle it just fine. If you do forget the call sheet and know the sequence do NOT tell the pilot,,,, I told him I had the wrog sheet just as he was completing his takeoff. Needless to say I think it freaked him out a little and although he did what I said to do, he was distracted by concerns about whether or not I really was calling the right sequence. Overall he flew well and it turned out fine. We laughed about it after. One of those memories I will always have to laugh about.