First, review the judging criteria of Table Topics Contest:
1) Speech Development (Opening, body, close, organization, smoothness)=30%
2) Effectiveness (Logic, directness, enthusiasm, achievement of purpose, audience response)=25%
3) Physical (Appearance, body language)=15%
4) Voice (Flexibility, volume)=15%
5) Language (Appropriate to speech, purpose and audience. Good grammar, pronunciation and word selection)=15%
So if you are already an eloquent speaker, half the battle is won and you will score better in body language, vocal variation and excellent command in English.
If not, you can still pip to win by speaking more clearly and intelligently on the topic to win the hearts of the audience and judges with your logic, appeal and wit.
Time is a factor, with 2 minutes, you need to have both coverage and depth and stand out from the other contestants. And if you go overtime, 2 minutes 30 seconds, you are out.
Be prepared for the unexpected as in "silly" or "mouthful, confusingly long" or "incorrect grammatically" topics. Examples like:
a) "Is a mother or a father a better parent";
b) "War is bad yet unavoidable, yet how can we teach our children and how to make our school education system to complement that"
c) "Baby is more important than love and money, it is glue in one marriage"
Practise. Have someone or your club members throw different topics at you and you can practise answering them. Or you can mentally make up topics and response to the topics in front of a mirror or video camera. Or visit different clubs and volunteer to be the first speaker during the table topics session.