Think before you buy
Not everything makes an appropriate gift and it's important to match the right present to the right relationship. Clothing for your girlfriend is tricky; you'd better know the exact size. (Too small is depressing and too large, insulting.) A gift certificate may be perceived as too impersonal for a loved one, but very appropriate for an employee. Perfume is a dangerous gift for anyone unless you know for sure it is their favorite.

Don't jump the gun
Getting a head start on your holiday shopping (I've known people who boast that their gifts are bought and wrapped by August) is commendable, but not always practical. It's always possible that the recipient will have developed an interest in something completely different by December, or, worse, have already purchased it for themselves. This is applies especially to books, movies, and music. However, one-of-a-kind items bought in a foreign country or an antique shop are generally a safe bet.