Practice speaking extemporaneously. Have your students start in a circle and begin by asking them to tell a story in the round, where each student makes up one sentence of the story before handing it off to the next student. Slowly build this up as your students' confidence increases to have each person tell a one minute section of the story. A game timer can be helpful to make this part more fun.
Teach through conversation. Set up flash cards face down with likely topics from the TOEFL test (see the TOEFL FAQ in the resources section of this article and then click on the "Sample Test Questions" link to download). Have a pair of students face each other across a table to take turns picking up a card and speaking on the topic. The pairs can take turns asking questions and offering feedback.
Take the TOEFL practice test (you can find one in the resources section of this article). The more time spent practicing the test taking habits, the better the students will perform on the test. Attempt to recreate the environment of the actual test where they can have uninterrupted time and the ability to take notes.