How to visit New Zealand
New Zealand consists of two Islands, The North Island and South Island, so complicated isn't it.
The north Island is the most populated and most travellers would arrive at Auckland airport and then travel south, I would recommend that you should travel North to the beautiful sub tropical Bay of Islands, it's approximately a four hour drive from Auckland to Paihia or a two hour drive if your with a Kiwi...they drive like crazy, dangerously mad.
The best advice I can give you is to fly into Christchurch in the South Island and then down south as far as you time will allow you, the South Island is by far the most beautiful of the two islands, you will see the real New Zealand it's that picture in your mind of how you envisage New Zealand.
Best time of year would be after December in both Islands great weather is practically guaranteed, the downside will be that this is the period when most Kiwia are on there long summer holiday which makes accommodation more expensive and difficult to locate.
Its a relatively safe country apart from driving, you just need to be a lot more alert, public transport is limited and I really wouldn't recommend hitch hiking it's far to dangerous.
You will need a travel visa, and pack light, New Zealans lifestyle is very informal, tee shirts and shorts are the usual form of dress.