The most important aspect is what is known as proof of his "bona fide" status. This is all about being able to convince INZ that he has the means (a flight ticket or money to buy one) and the motivation to leave NZ before his visa expires . This last part can be any or all of evidence of a job to which he can return (letter from employer), a partner and maybe children that he will be leaving behind (photos, marriage certificate), that he owns property or has a tenancy agreement in his name, that he has travelled abroad before and always complied with visa requirements. Be aware that he may only get offered a Limited Visa which would require him to leave NZ before applying for any further visas. See
http://www.immigration.govt.nz/opsmanual/34338.htm