What's your price range? When are you planning to go and for how long? Do you have hotel points (or airline miles that can be converted into hotel points)? Do you like staying in larger chain hotels or would you prefer a boutique hotel? Charming or cutting edge style? Are you interested in staying in an apartment?
For areas, I'd recommend the Marais (it's busy but not raucous), the area around Trocadero and the area around Opera and the large department stores.