Most "Wiccan etiquette" is just plain common sense just as etiquette is in general. There are a few areas you may find unfamiliar though, so it helps to have some guidelines to avoid social and magickal faux pas.
1. Circle etiquette:
We like to wash away all the physical reminders of the mundane world. A clean robe and clean body shows courtesy to others and reverence for the Gods. The Ritual bath is not for cleansing the body - it is for purifying the mind so please bathe ahead of time. A ritual bath complete with incense, candles and magickal oil may be provided. Other types of ritual cleansing that may be provided are a handbath, finger bowl or smudging. These are not substitutes for physical cleansing. While it is not proper to wear strong smelling perfumes or oils to circle which can overpower the incense there is no rule against deodorant (some how this rumor has gotten loose in the pagan community).
There should be no gossiping about others or other negative talk before circle. If you have a problem with someone else, talk to them or the Priest or Priestess privately. No talking while waiting for your turn at the ritual bath. This is the time to begin centering and grounding.
When in doubt about anything ask the HPS or HP of the circle before the ritual starts.
2. Jewelry, Tools, Etc.:
Please ask (and wait for an answer) before touching anyone else's jewelry or magickal tools or Tarot Cards. It is tempting to touch when a friend shows up with a pretty new necklace or chalice, but remember: they may have gone to a great deal of trouble cleansing and charging it for a particular purpose and may have to do it all over again if anyone (even a friend) touches it.
While the only hard and past rule in Wicca is "An ye harm none do what ye will", most pagans ascribe to the rule: "Don't haggle for magickal tools". This is a natural extension of "Harm None". When you haggle the seller may feel compelled, against his or her own will, to drop the price.
4. Driving & Bumper Stickers:
Bumper Stickers are wonderful ways of letting the world know who we are and how we feel about things. Display your, "Born Again Pagan" and "The Goddess is Alive and Magic is Afoot" proudly. BUT, please think twice about giving rude hand gestures, or allowing others in your vehicle to (even to deserving jerks), while you are declaring your "paganness" to the world. Like it or not, when you are openly pagan, you represent all of us. Please do it with pride AND decorum.