Traditionally, female flamenco dancers wear their hair long - and that's one tradition that doesn't appear to have changed in nuevo flamenco. It's rare to see a flamenca with a short hair style!
Also traditional is the use of hair ornamentation. The stereotypical image of a flamenco dancer is a women with a red rose and an ornate comb in her hair. Contemporary dancers may wear no ornaments at all, but if you're in a more traditional school, chances are you will still be expected to put your hair up and decorate it appropriately.
The simplest decoration is a beautiful fake rose - or perhaps two or three in a cluster. Make sure they're well secured by several pins!
I don't recommend using hair combs unless you can be sure they're anchored securely - I've seen too many of them fall out on stage, causing a hazard for other performers. If you're dancing up on a stage, they're not that visible anyway.