How do I make sure my new website is not blocked in China?

If your targeted visitors are all from China, I recommend you consider hosting your site with a webhost in China for the following reasons:
1) less likely to block
2) closer to your audience (generally, you want your servers to be closer to your audience to decrease server loading/routing time)
3) SEO - most likely you'd like to be decently "searchable" in search engines and having a Chinese IP would make you more "searchable" to your Chinese visitors and search engines

Unfortunately, the only way to know if you're blocked is when your visitors complain they can't get to your website.

We block millions of websites either completely or partially and it's virtually impossible to provide a complete list of blocked websites. As a rule of thumb any website that hosts content which contradicts CCP position on any issue will be blocked by us. CCP is always concerned about the type of influence that foreign websites are likely to have on Chinese citizens. Thousands of paid web commentators (50 cent party) keep looking at all Internet Forums and websites. Any website having a content that contradicts CCP position will be automatically blocked once it is reported by our 50 centers. Where it is not possible to delete the comment or block a website altogether, our 50 centers will tactfully try to argue the case in a way to limit the damage. Many 50 centers are active on this forum as well. Accessing the blocked websites by any means, be it VPN or proxies will be construed as violation of Chinese Censorship Laws. If you are a foreigner visiting this country, you are expected to observe Chinese Laws failing which a serious case will be made against you and you will be certainly deported. If you want to learn more about the intricacies of Internet Censorship and Policing in China, see MY answers to the following questions

You should choose a web hosting company which is not blocked in China , you can check review of top ten web hosts at website like http://aplis.net/ .

You can't. It'll be impossible to stop them, without doing anything illegal. Just avoid anything that'll piss off the CCP cronies off. Like for instance, you don't want to mention that the CCP ruthlessly MURDERED harmless, peaceful protesters countless times.

Say a few things about how much you support communism.

Ok it is easy to slove this proplem .. open skype programe and add any one from china and ask him about you're web site ..

They will only block something that is critical of China's behaviour or deeds, or anything negative towards China.