It is never easy per say to improve your speaking in order to get a higher test score quickly. But there is a way you can do to improve the overall performance to a certain extent. If you were never really practiced in this way, it should serve you very good.
The Technique I am going to mention here is very easy. Draw a Cross and divide a piece of paper to four blank sections. Now write Grammar, Pronunciation, Organization and Vocabulary in each section, and save it for later use.
Find yourself a software, one like audacity as I have mentioned here before to record your response. Play your response again and again to check for mistakes and categorize them into the paper divided to four sections previously.
Make sure you do the same oral task again and again until you avoid all the mistakes listed on the paper.
This may seem painstaking, but it really improves your oral response to a full extent of what you can achieve during a very limited period of time.