This spot is probably a bit better than the average on the North Island, and it is still suitable for everybody from beginners upwards.
The beach at Mangawhai Heads is just a thin strip of sand and you will have to paddle out from here across the harbour to get to the spot. It is all public access and is about 1 1/2 hours drive from Auckland.
The best conditions are found when the wind is blowing from the north-west, west, south-west, east or north-east and the swell is coming from the north, south-east, east, or north-east. It will start working at less than 1 m and hold up to about 2 m or 2.5 m, and you need to catch it on a rising tide at either mid or high tide positions. It is a reef break, both left and right, and although the waves are pretty ordinary in terms of speed and power they are hollow which makes it a bit more interesting. Length is about average and will reach up to 150 m on most days, and if you catch it on a good day you might see it reaching well over 200 m.
The area has a decent selection of holiday rentals if you want to stay, and of course you can camp if you prefer. There are a few restaurants and places to eat dotted about and most people make it a day trip from Auckland. The beach area doesn't have any facilities on it but you can at least park close to the shore.
Watch out for the rocks that make up the break, and keep one eye out for sharks although they tend to be quite docile and if you don't annoy them they won't bother you.