In class, my students do a lot of mock speaking exams.
Picture description is fairly easy for the student to control as he is on his own, with no interference from the teacher and he can, to a certain extent, know in advance how he is going to structure his description. No worries here!
(See some useful guidelines and techniques for Picture Description here)
The Interaction between the teacher and the student is the part of the exam that causes more stress and anxiety. The student doesn’t know what he’s going to be asked about and sometimes students find it difficult to get started and gather their thoughts. Some students are very clever and very quick at organising the answer in their minds; I would say it comes naturally to them, while other students need more time to think of a coherent argument. Unfortunately, most students fall into the second category and they need all the advice we can offer them.
There are some techniques you can use to give yourself some time to think about what you are going to say, but I would advise you to use them in a sensible way and make sure you don’t answer every question with a filler, as you will certainly run the risk of sounding very unnatural.
♥Use the typical filler sounds:
-ah, mm, um, uh,
♥Repeat the question:
-” Umm … What would be my ideal job??? Well…”
♥Pretend you haven’t understood the question:
-” Could you repeat the question, please?”
-“Sorry, I didn’t hear what you said. Could you repeat the question?”
♥Express a lack of opinion:
“I’m afraid I don’t know much about it!”
-“It’s difficult to say!”
-“I have never really thought about it!”
-“Well, I don’t know, but I think /people say…”
Hope it helps you!! And remember USE WITH CAUTION!
If you are studying, yes, “studying ” for the oral test, you might be interested in this other post. Tips to Score High in the Oral Test
I’m never in the mood to start teaching straight away as some students have not bought their textbooks yet, you have some information to give, some forms to be filled ..etc, so I usually end up having less than half an hour to get them into the right mood for learning. That’s why I am considering using some of these activities from 
not say “three!”. With the number “30”, the students must also clap once, and with the number “39” students must clap twice, because there are two instances of the digits 3, 6, and 9. 
get 10 correct words, that team gets the square. The first with 3 in a row wins the game. With more teams use a 4×4 grid, teams have to get 3 or 4-in-a-row. Good for younger learners.
to the team member at the front of the class. The first student to guess the word wins a point for their team.
(or several words) starting with the given letter for each category. For example, imagine a class is using the example categories above and the letter “s”. Correct answers would include “shirt”, “salad”, and “Spain”. If a team gives a word for each category in under a minute, they get a point. The team with the most points wins