So there are 5 main principles of flag design (taken from Good Flag, Bad Flag):
[li] Keep It Simple - The flag should be so simple that a child can draw it from memory…[/li][li] Use Meaningful Symbolism The flag’s images, colors, or patterns should relate to what it symbolizes…[/li][li] Use 2-3 Basic Colors Limit the number of colors on the flag to three, which contrast well and come from the standard color set*…[/li][li] No Lettering or Seals Never use writing of any kind or an organization’s seal…[/li][li] Be Distinctive or Be Related - Avoid duplicating other flags, but use similarities to show connections…[/li][/ol]
*** Red, Blue, Green, Black, Yellow, White**
There are more general guidelines that relate to the 5 principles:
[li] No solid color flags (it’d be unidentifiable when printed in grayscale).[/li][li] Stick to proportions between 1:1.5 - 1:2.[/li][li] Avoid signals on the fly end. They’re hard to see when flapping in the wind and they also will experience wear and tear first.[/li][li] The canton (upper left) is traditionally the most significant/important area.[/li][li] Ensure the flag is recognizable at different scales (such as a lapel pin).[/li][li] Aim for timelessness.[/li][li] Heraldry traditionally has animals look towards the hoist.[/li][li] Avoid two-sided flags; they are harder to recognize and much more expensive to make.[/li][li] Diagonals are often used for former colonies.[/li][/ul]
I looked at a bunch of the submissions (generated at random from 10,000+). I found this collection of traditional Maori symbols really helpful and interesting. The following are some examples of (IMHO):
1867-69 Flag of New Zealand – … Yeah, no. It’s the existing flag, made worse!
Curves – This seems like it would immediately be called the Tits or Ass/Arse Flag.
Shell – It’s a lovely shell, but too intricate for a flag, IMO. Also, gradient fabric would probably add a lot to the expense.
Truely NZ – You just stuck a fern on the original flag, dude.
Our Land (green reverse) – Way too many separate elements/devices plopped onto a flag.
Where We Stand [4 separate designs] – The bottom left one seems … ok … to me, but the curliques look too curliqued, to me. They, along with the angled stars on the right two flags, just seem like they will be incredibly dated quickly.
THE "LOOKS TOO MUCH LIKE A SPORTS TEAM’S LOGO"
TRUE KIWI v1
Hei Matau (The Fish Hook)
SHOWS SOME PROMISE, BUT MAJOR FLAWS
Pacific’s Triple Star – I like that PJ put a lot of thought into the symbolism of each element/device and the red stars relate to the old flag. The problem is that there’s no clear indication of where the top and bottom stripes end because they match the white background (which could happen on a really cloudy day, too).
Aotearoa flag 3 – I like the stylized koru and the white circle adds interest without being too detailed. The white background is still defined by the cross and I like the kind of subdued red of the koru. Buuuut I think the blue doesn’t go well with the red and the black is too dark of a color to see surrounded by other dark colors. I also don’t like that it symbolizes their “nation’s sporting identity” (nothing wrong with sports, but for timeless national symbolism? No).
SOUTHERN CROSS AND FERN 1 – I like the abstracted, angular fern and diagonal line. But it looks just a bit too much like a sports team or Olympic national team’s design (perhaps Team Canada or a hockey team?). It’s also on the fly side, so it’ll get torn up quickly.
Kiwi Fern – the concept is cool and a great way to work in two symbols with only one element! The kiwi fern is too realistic (heh, that sounds ridiculous) with the leaves looking like actual fern leaves.
Kiwi Fern (version 31) and Kiwi Fern (version 20) – This kiwi fern is a much better style. I like the v.31 element a bit more because it’s more abstracted with the straight lines (which could also kind of symbolize a fish skeleton/fishing?), but the v.20’s curved green field is a nice idea and continues the flow of the kiwi fern.
Three Islands  I think this is a striking design and I like the 3 stars for 3 islands symbolism; the third star being smaller like the tiny 3rd island also adds visual interest while harmonizing with the others. I don’t like how there’s no explanation for the green and white triangles, though. I’d also like to see it with the green on the bottom instead.
NZ “Canting - Heraldic” Version 8 – Okay, I just freaking love this design, even if it’s not the best for New Zealand (though it has the Southern Cross). It uses a great deep and warm yellow and is graphically striking.