This is a well known theatre exercise which is extremely effective for encouraging controlled but spontaneous interaction in ESL classes.
STEP 1 PRESENT
Begin by presenting a list of debate expressions such as those listed.
STEP 2 MODEL
Model a discussion. Choose yourself as conductor and 4 other students to be conducted. First, the conductor presents a topic. He then selects a student and an expression for the continuation of the discussion.
Conductor: Elephants shouldn't be allowed into Bangkok. Student B "Furthermore"
Student B: Furthermore, the government should fine their owners.
Conductor: Student A "On the other hand"
Student A: On the other hand, people in Bangkok are very generous when they see elephants.
Conductor: Student C "For example".
Student C: For example, when they see elephants they feel compassion and give them food and money.
Conductor: Student D "You may have a point".
Student D: You may have a point. Nevertheless, the pollution and traffic are terrible for the elephants' health.
STEP 3 WRITING
To reinforce the use of these expressions further, follow this activity by a debate or writing exercise