This is a variation of what I was taught on my course (amended for personal taste) and is what I have used.
"I want you to indicate ball in and out of play for all throw-ins, corners and goal kicks. I want a nice clear signal showing that the ball is out and the direction of the throw. I will always go with you (I don't always but...). If you are unsure of the direction, look to me and I will indicate. Go with my signal. Any offside offences, remember that the offside player has to get involved in play (I don't further elaborate). Give a nice strong signal to indicate to me. The final decision will be mine as I may be in a better position to make a more informed decision. I will indicate that I have seen the flag, but if I don't whistle, I haven't given it. I will tell the captains to play to the whistle rather than the flag (and I do)."
Hope this helps.