What's the secret to establishing good contacts?

No, I am not referring to social networking when I mention contacts, but instead addressing the area where the proximal surfaces of teeth meet each other. Contacts between teeth should not be a "point contact" if at possible.  A proper contact can prevent interproximal food impaction.  Not only is food impaction annoying, but can cause gum disease and can even lead to recurrent decay.

When preparing a crown preparation for my patients I also prepare the proximal surface of the adjacent teeth. I take a sandpaper disk to flatten the proximal surfaces of these teeth to help insure that my ceramicist can create a proper contact area for the new crown. This area varies depending on the tooth, but  posterior teeth should have a relatively broad area ( approximately about 2 mm in height and 3mm in width). Anterior teeth, since they are narrower on their proximal surfaces, have much  smaller contact areas (about 1 mm x 1 mm)

I test my contacts with unwaxed floss. I am happy with contacts that make a snap noise when the floss is carried through but do not cause the floss to shred. Also the floss should make a U shape when pulled back through the contacts ( since a proper proper posterior contact is at around 3 mm it creates this U shape when tested.)