VG has an article about the rules for how you are going to wear your national costume the right way, for a dress you wear only once or twice a year you see alot of creative solutions on national day and not all is very becomming.
1 Wear the head dress that goes with the national costume, this goes both for women and men (many break this rule, simply because some of the hats and shawls are strange looking and uncomfterble)
2 Use the right shoes, the ones that goes with the national costume. (when Mary visited Færøyene we could see she wore
pointy pumps the one day, a no-no, but she had the
right shoes the next day, even worse is white trainers which also has been seen, (not on royals) especially later in the day when people get blisters from the shoes they only use once a year)
3 Use the right stockings, wool or cotten, not nylon, check that you used the right color for your costume, usually black
4 Minimize the stash. Place the silver brooches where they are supposed to be, dont use the silver belt if it is not intended for your costume
5 Dont use other jewellery, no earrings or similar unless they are part of the costume
6 Make sure the skirt is the right length.
7 If it is cold wear white woolen underware, dont wear colorfull jackets to keep warm, If you dont have a shawl or cape with your costume you can wear a black jacket
8 If it is raining, use a black umbrella, some has started to make umbrellas with national costume pattern, another no-no
9 Natural look, dont use makeup or make sure it is very natural (also no plastic stash in the hair, fake flowers, bows and similar)
10 Only men are supposed to wear a knife with the national costume, that some women wear a national costume knife is a modern invention
http://www.vg.no/pub/vgart.hbs?artid=115833
And the 11 rule is that National costumes has a tendency to make even the slimmest of woman look pregnant, the reason is the heavy wollen fabricks they are made of, sometime it can be as much as 8 meters of thick fabrick in the skirt, as well as the waistes on them are often pretty high, giving some sort of semi empire look.
Then Norwegian royals has made several mistakes which has gotten them press and in trouble with the self appointed national costume police, Sonja often uses shades with her costume, she has placed the silver brooch wrong at one time, Mette-Marit rarely wears the headdress, and as a fiancè she wore a fake national costume for a private party which got her the frontpage
The palace did soem damage controll and pretty soon she and Haakon made an apparance both wearing the right thing. She has also been seen with the wrong shoes. Mette-Marit has 4 national costumes (one from before her marriage), Sonja has atleast 6 and Märtha Im not sure, the one she usually wear she has inherited from her grandmother Crown Princess Märtha. Normal people usually only have 1. Crown Prince Haakon has one from Fana in Bergen and Harald never wears national costumes because he wants to be neutral and not linked to a specific part of the country
foto: Hallgeir Vågsnes
Here she is wearing correctly her wedding present, a national costume from Hardanger with the correct head dress which it took 2 local women more than an hour to put on her
Mette-Marits 5 times on the balconny
and her 4 times at Skaugum, in 2001 the King and Queen was still living there
Pictures from scanpix and rex