One of the first factors crucial to second language acquisition is that the learner be placed in a low anxiety situation. Why is this? People naturally have what linguist Stephen Krashen termed an "affective filter," a psychological barrier that can impede learning. When a learner is either very anxious, under motivated or lacking in self-esteem, his affective filter goes up, and he has a very difficult time taking in or processing new information.
Therefore, psychologically speaking, one of the factors most important for someone trying to learn a new language is to find a situation that is low stress. If it is a classroom arena in which a foreign language is being learned, it is largely the responsibility of a teacher to ensure an environment that does not cause anxiety for the students.
As a teacher, how can you create a low stress language learning environment? One way is to involve a lot of fun and hands-on activities with language learning. When students are involved in games or activities, they will not be an anxious as if, for example, you are calling on students seated at their desks to one by one produce sentences aloud.