Nicky Hilton says every woman should have a signature scent they should always wear.

The 31-year-old fashion designer has written her own style guide book, '365 Style', in which she gives her tips clothing and make-up.

Nicky - the sister of Paris Hilton - is adamant girls shouldn't change their perfume and stick with one brand that the becomes synonymous to them.

Speaking to the New York Post newspaper, she said: ''Trademark your look. Individualise like von Furstenberg's created wrap dress. Nothing's original. Personalise your style. Pick a signature scent. I've worn Quelques Fleurs forever. Let one item be the star. Save your hemline. Fold it under. Someday you may want your expensive dress longer. And if you're busy on top, be simple at the bottom.

''This society all tries to dress like a young superstar. The red carpet does no sleeves, no ball gowns. Nothing original. Everything should look effortless, not like trying so hard. And better to be under-dressed than overdressed. Also appropriate. A prom is not casual. A beach party is not black-tie.''

Nicky hopes readers will learn a lot from her book and admits she has been making notes for it for the last 10 years.

Discussing the writing process, she explained: ''I filled 20 notebooks, I've been in the industry 15 years, modelled, created handbags, jewellery, worked with designers and stylists. This took two years to write, 10 to learn, and I've collected ideas and anecdotes forever.''