Come to class early and talk to people. When you see recognizable faces in the hall, stop and talk. But it is interesting to note that most classes are set up to efficiently deliver punishment. Points are taken off of tests. Papers are graded by marking all of the mistakes.
People respond best to personal praise.
Try to make test and assignment grading schemes incremental rather than decremental. A simple question can often be enough to deliver the criticism, without the student ever even realizing it. Given the freedom to explore and try things, people will take advantage of it. This trait is the basis of the research process, and should therefore be encouraged. Cookbook labs kill curiosity.