Actually it depends on what is your strength. If you good at math, you can go take part in math olympiad competitions. If good at sports go for state competition first and if you win it you can go to national level. There are many competition s at state level just have to ask your co-curriculum teachers or your form six friends in other schools or even internet and newspapers.

I am going to study in NTU this august if I got any scholarship. So far haven't get any news yet from the scholarship i applied. Most of them are provided by sg like Singapore scholarship, ASEAN and so on.
Thanks, so far only shortlisted for several scholarship agencies for interview. Hmm if sports then there are many basketball, badminton, football at state level organized only for form six ( almost every year there is ), if you are a physics student you may go and participate in some competitions related to your study like robotics competition. Anyway you have to let me know which field you are strong in only i could help you. 

well maybe you can take part in robotics competition, amphibious electric vehicle competition, math olympiad, physics olympiad etc.