Depends upon the business and your level of network connections. If you're looking into professional services a network is just about a must since Singapore is actually a very small community and everybody knows everybody. At least some contacts into the local branches of MNC's is a necessity.
If you are a foreigner/white, you'll have a very difficult time breaking into Chinese business... they have a very tight network themselves (I'm referring to a professional business of some sort again). I've got a successful business and my clients are all multi nationals.
I know folks have started restaurants that are very popular... if you've got a theme and experience you stand a good chance of making a go.
In short, you've got the same hurdles as starting a business anywhere, plus the added problems of dealing with a close knit community and cultural preferences/differences. On the other hand, Asia provides great opportunities as well as lots of investment capital continues to pour in.
Singapore is a relatively easy place to start a business, whereas in other countries, the beauracratic process can take weeks or months, it takes literally minutes in Singapore. You can do some market sizing at the singapore stat board website and ACRA for the process of incorporating.