Is it a good idea to go to a university just because of its high international ranking?
Is it a good idea to go to “National University of Singapore”


It may be. I have recently visited NUS, and talked to a lot of smart faculty and some truly outstanding students. Personally, I can only recommend both NUS and NTU Singapore. Singaporean universities are well-funded and offer a reasonable research environment. Singapore itself is also a nice place to live, with a quite interesting mixture of different cultures, lots of food, high standard of living, etc.


  just because of its high international ranking?


Oh god no.

If you want to go to NUS, then because of the reasons stated above. It think convincing the world that university-level rankings are a good thing is the largest disservice that the US has done to research. Let me make this clear - if you graduate from NUS and do uninteresting research, nobody will hire you. If you graduate from another reasonable university and do good research, you will find a post. 


  Do you think that going to the NUS can help me to get accepted into world top universities in the future?


Only for the reasons stated above - NUS has an environment that certainly enables you to do world-class research. For this reason, NUS may certainly help you get into a top university, but it does not make you accepted. The hard part (being a good researcher) will still be required from you.