When it comes to gifting etiquette, many people say you should avoid giving a fragrance unless you know it is something that person already uses. We are not most people, so we say poppycock to that rule. Giving the gift of scent can be a great way to show someone how well you really know them, and introduce a new perfume into their repertoire.
If you're unsure of what scents your intended might like, a good rule of thumb is to check out which ones they already wear. This will give you the idea of what scent-family they're into (floral, citrusy, musky, etc.) and help you hone in on some related eaus they might enjoy.
However, there is one scenario you should skip: If the person you are thinking of buying for has a signature scent and wears nothing else, chances are good that they're not in the market to discover something new.