While code has his points about the scholarship thing not being for everyone, sometimes it's the only route for people to get overseas. As to why overseas, I suppose everyone has already heard the arguments about why overseas. =D
In any case, dude; what I would do if I were in your shoes:
1) Think about what course you want to take. Be very sure.
2) Be the typical RJ student (hee hee) and apply for all the scholarships. Of course don't be too unselective and apply for nursing scholarships if you know you will NEVER be a nurse, etc. Do not limit yourself to just DSTA and PSC - though from experience you do stand a chance in getting DSTA still. PSC to be frank, not so. Besides, do find out more about the different scholarship - you're from RJ, milk the most of it, there are so many scholars amongst your seniors. From what I know, DSTA isn't all that it's made out to be, but I'll leave it at that. Some of the stat boards have pretty good environments, friendly and all that, and opportunities are also boundless. Once again, it's what you make out of it.
3) You should at least get a few interviews, keep calm, and personally my view is not to prepare much for it. Think before you speak, that's really all you need - the more you attend, the better you'd get at it, heh.
4) If you do not get interviews and all that, think about what you want to do in Singapore - hope this doesn't get your goat or anything, one must always prepare for the worst while hoping for the best (of course don't let this get you down at all).. It's really not the end, as so many before have proven.
5) All the best! I repeat - just make the most out of what you've gotten , and everything will resolve itself in one way or another. Good luck.