What do you think should be done to prevent copyright violations?

There are three main categories of copyright violation, each best handled in its own way.

Large-scale commercial infringement, such as sites allowing download of current movies, is too big of a money-maker to convince people to voluntarily stop. In this case, civil and criminal prosecution may be the only way to prevent it.

Individuals participating in P2P sharing networks are often doing so because it's easier, cheaper, and more convenient than getting the same materials legally. The best prevention here would be to work to create legal channels with the same flexibility. Note that illegal sharing of music dropped off significantly when iTunes became prevalent.

Individuals unaware that their activities are infringing may simply need to be educated about how copyright affects them. Both the economic impact and moral issues can be used to explain how infringement hurts artists.

At the moment, rightsholders tend to try to lump all three groups into one pile and treat them the same way, even though this has been proven not to work (DRM is an example of this). They need to acknowledge the differences between mass infringement and a kid with a flash drive.