While this site (and the list below) is geared to events set in 1300-1700 England, what's here is well suited to just about any event you'd want to visit.

Blending In
• Do your homework. What I mean by that is don't go to a 1500's faire dressed as a musketeer, or dressed in wimple and gorget and flowing robe. By the same token, don't dress in a black robe and claim to be a Franciscan monk (or brown claiming to be Benedictine).
• Dress appropriately for the season. A lot of costumed patrons show up at renaissance faires wearing a cloak because that "defines" the period for them. In August, it looks ridiculous.
• If you're not going to dress from head to foot, don't dress up. Don't wear tennis shoes with your garb. Performers can spot a costumed patron 95 times out of a hundred, and most of the time the giveaway is the shoes. Glasses run a close second.
• Another giveaway is the accessories. There usually aren't any. Your average street performer is carrying his or her entire inventory on his or her person. That means a belt to hang things from and pouches to hang from the belt. Also bring something to eat with and out of, and something to drink from. Eating and drinking out of paper with the festival logo marks you.

  Interaction

• Faire performers are, by and large, the most giving people you'll ever meet, but they have a very low tolerance for bullshit. What this means in practical terms is: if you want to talk to a street performer, dispense with the "What ho! cousin! Prithee, tellst thou me how fares thy day in this, the grandest of all shires." Instead, try normal, everyday english, and speak formally, respectfully. You'll be guided where to go from there by the reponse of the person you've approached.
• Make sure the performer isn't already in an interaction with another patron or performer. Interrupting is impolite anyway - you compound the crime if the performer is busy doing his job.
• Keep your interactions respectful. There's good reason for this: many performers are trained to do what they do and they get to do it every weekend, so they're fresh and well practiced. That makes it a little like challenging Wyatt Earp to a shootout; you may make it out alive, but you'll be full of holes.
• There's another reason to stay respectful: if you're a jerk, most performers won't even bother with you. The goal is to have fun, and that means fun for all persons involved.
• Always remember: this isn't your show. You paid to get in. Leave the performing to the performers. (There are some faires that will escort you from the premises if you get caught forgetting this rule. Kansas City is one.)