As in any other court, the fashion was decided by the Queen. When it came to the hair styles of the Tudors the styles changed as often as Henry VIII's wives.
Long, flat hair:
Most women of the Tudor time rarely cut their hair which meant that they would end up with very long hair. It was the norm to conceal the hair under a hood or a headdress but there was exceptions (as always with fashion): on her wedding day a woman could keep her hair loose which was also the case at coronations. Anne Boleyn and her daughter, Elizabeth I both had loose hair at their coronations; Mary I had loose hair at her wedding. Both Anne Boleyn and Catherine of Aragon is said to have had hair down to their thighs.
The long, flat hairstyle was specially favoured by Anne Boleyn and in the most famous portrait of her, you can see that her hair is flat.
On this, Elizabeth I was different from her mother. Elizabeth preferred to have curly hair - which immediately became fashion among the ladies at court. Nowadays, women just use a curling-iron to achieve a perfect curly hair but in the Tudor era, women had to use a different strategy. The Tudor ladies used hot tongs to curve their hair into the fashionable hairstyle favoured by the Queen.
Having your hair hanging loose was a sign of virginity and was mainly used by young women at their weddings. But as soon as a Tudor woman was married, it was no longer prudent to have loose hair. Instead, she was to have her hair in a bun - a practical arrangement that made room for the elaborate headdresses at court.
It was very fashionable to have a high forehead and women would even pluck their hairline back to achieve it! Also, it was in fashion to have your hair arranged in such a way that it would not cover the forehead.