I'm not asexual, but this is a very useful summary of how to successfully use a label.
"Asexuality is like any other identity- at its core, it’s just a word that people use to help figure themselves out. If at any point someone finds the word asexual useful to describe themselves, we encourage them to use it for as long as it makes sense to do so."
http://www.asexuality.org/home/overview.html