A trade mark is a form of government-granted monopoly. Because of that, the requirements for a trade mark are set out in the Trade Marks Act 1995.
The first basic requirement is that your proposed trade mark must be able to distinguish your business (within the relevant class of goods and services) from other traders. Your application won’t succeed if your proposed trade mark is something that fair-minded businesses would want to use. Common examples include a descriptive word, a geographic name or a common surname.
The second basic requirement is that your proposed trade mark can’t be too close to other trade marks (eg registered trade marks, pending applications, or businesses with known reputations).
It’s possible to get past these requirements if you’re already using your trade mark. But you’ll have to prove that you have a reputation in the your market. However, that’s an expensive and potentially tricky job. It’s far easier (and less expensive) to simply choose a trade mark that fits the two basic requirements above.