When arriving in NZ, Immigration is very quick and friendly. As long as your passport is in order and you haven't been convicted of any major crimes you will be fine.
Customs is also quick, but a bit more intensive. Your luggage will be x-rayed and it will be sniffed by bio-security dogs. You might be pulled aside to answer questions - main concerns, have you been on a farm recently, are you carrying any food.
If you have hiking boots and/or camping gear it might be inspected.
To make things easy - do not carry any food with you - no fruit or snacks off the airline tray. If you have packed anything which is food, fresh, raw, dried, packaged or not, it must be declared. If you fail to declare it, it will be found (those clever wee Beagles can smell if an apple was in your bag a month ago) and there is an instant $400 fine.
also ensure your footwear is free of mud, dirt, grass seeds etc. Any camping or fishing gear must be spotless.
why all the fuss? We don't have rabies, lyme disease, foot and mouth disease, mad cow disease, ticks etc and bio-security is working hard to ensure we remain pest-free.
I am usually through Immigration and Customs within 20 minutes. It can take a few minutes longer if a few planes land at the same time.