Cool Video article of this piece written by the late Wong Shun Leung, great pictures too.
http://www.youtube.com/watch?v=1BBT3XD1QJY .
Some fine advice IMO, some points of interest:
1) chi sau skill is for when your attack meets an obstruction, we don't stick to the hand otherwise you will chase hands (go somewhere other than towards your opponents center).
2) you will more than likely be hit while you are fighting, to tell your students they won't or other such notions of invincible skill is shameful.
3) be patient in a fight and hit when your opponent doesn't expect it, when they are hitting you (requires good timing) and within one step range, therefore setting up a good follow up for yourself.
enjoy,
James