Mistake 1: Spending too much time describing the picture
Take note, there is no longer a 'Picture Discussion' segment for the 2013 O Level English Oral Exam. Spending too much time on the Picture (or visual stimulus) will not be a good idea.
Mistake 2: Forcing a link between the picture and the conversation topic
Sometimes, candidates are unable to identify the link between the visual stimulus and the conversation topic; and they end up creating an impossible or illogical link between the two. Do not do that.
Mistake 3: Speaking too fast
Speaking too fast will also result in the candidate "tripping" on his/her own words. Although it is understandable that candidates can get quite nervous during the O Level English Oral Exams, it is important to keep your composure and maintain a proper reading and talking pace.
For those of you still hovering around an average grade for O Level English Oral, it is not too late. There will be a crash course which you can attend.