Sorry, for the long delay since I last posted, I am currently reworking the site.
I have seen a lot of chisao, sparring and push hands over the years and one thing that I am constantly surprised about is the number of people that look down when they practice fighting. Actually the same thing happens in salsa as well.
I can understand that a beginner is so concerned with what he or she is doing that they will look down at whatever body part they are moving, but this should be strongly discouraged.
In a fight you have to fight the man, not the moves. Your attention must be firmly on the source of moves. It is possible to do this while looking somewhere else, but it is much easier to just look the direction that your attention is focused.
The body will unconsciously follow where you direct your attention. This means that the body follows the direction of attention. Your eyes usually reveal where your attention is. If you look down, you will go down. Your stance will most likely be unstable.
If you focus on the opponent, then your body will be directed in all movements to pull toward that direction. This is ideal.
It is not enough to have the eyes open in the direction of the opponent, actual intent has to be there. By "intent" I mean you have to actually be looking. You focus on the other party rather than what you are doing. This creates interaction.
One way to look at it is socially. If I approach someone and tell a canned joke or story without focusing any attention on them, it will probably not get much attention or laughs, regardless of how funny the material is. On the other hand, if I relax and actively listen to someone while I make the jokes that naturally occur to me in the moment, I will get a better reaction most of the time. I will also get better at it the more I do it.
Another way I like to look at it is by thinking there is no such thing as preparing or practice. Each time you spar, fight, chisao, wrestle, dance or whatever, its the real thing and should be interactive. Your partner or opponent deserves your full attention. In the doing of the actual activity, you get better. Your eyes are the best indication of where your attention is in the beginning.
Oh, and one last point because I am feeling snarky. Occassionally in wing chun, people like to wear blindfolds to show how awesome their "sensitivity" is. DON'T DO THIS! It misses the point and is extremely undignified. If you want to try closing your eyes sometimes, do so, and do it with them open as well, but leave the blindfolds to the kids.