Starting a discussion about the topic (possibly based on visuals and titles). In this sort of exercise students are asked to make a discussion about a set topic.
Brainstorming. In this activity the students are asked to predict vocabulary that is associated with the set topic and the teacher is supposed to write them on the
board. Another form of brainstorming activity can be making mind maps.
Game. A nice example of warm up activity where either the students or the teacher mimes the words and the rest of the class is supposed to guess the meaning.