Here are some common tips:
Angle the deck downwards slightly.
Keep your right fingers together and cover as much of the deck as possible.
Be loose and fast. (Although a pass doesn't always have to be fast).
Practice in front of a mirror from many angles, and also webcam.
Experiment with cover/disguises (thumb sweep, rock the deck, make eye contact to misdirect).
Always make it as small a movement as possible.
A minimum of noise is necessary - if they hear it - they'll know you did it.
Practice constantly and it will pay off.
Hope that helps you.
These are a couple of my passes:
http://www.youtube.com/watch?v=-QQ8j9g7BMw
http://www.youtube.com/watch?v=iN0_AOe4Xvk
I'm still AH, so its not upto pro standard. But I am getting there.