At a RenFaire, you might see that there are food and drink booths, some vendors, stages, and guilds (aka "living history"). You can take a few circuits, taking in each of these as they appear interesting, and call it a day. That's OK, but I think there's a better way.
A RenFaire is participatory improv theater. It's a place where you can talk to anyone, as long as you're respectful. You can start a conversation with anyone--guild members, vendors, patrons, adults, kids (make sure their parents are OK with it)--and have fun.
When I walk around a busy RenFaire, I put out a conversation starter to someone every few dozen steps. "Good day!" or "good morrow!" are the easiest ways to start. Some will ignore you, more will just reply without looking, but one in half a dozen will give you active attention.
If you get someone's attention, start a conversation. I use, "Are you enjoying your day at the faire?" a lot, followed by asking what they've seen or what they like best. Or I admire their fashion choices: "That's a beautiful shirt/kilt/dress/earrings/necklace/..."
You can make things up: - "I'm on a quest to bring someone to the king/queen/duke/...", or - (whispered) "There's a rumor that a dragon is ravaging the village, watch out as you get close to the warrior's encampment..."
You can ask questions: - "What tartan are you wearing?" - "I need to complete a quest to gain my knighthood. Do you have a quest for me?" - "Pray tell, do you know what a 'Scotch egg' is?" - "Truly you wear fashions from a foreign land, from what country come you?"
Wear something striking. It can be historical, but it doesn't have to be. Wear a big silly hat, or a loud Hawaiian shirt, or a Star Trek uniform. Anything you wear out of the ordinary gives the other fairegoers something to talk to you about.
Learn a few facts about the faire's place and time. A few facts go pretty far. If you know that it's 1603 and King James I just ascended the English throne after Elizabeth I died, you can stretch that into multiple conversations. Others will know the history better; play along.
Tiny gifts to give fairegoers are great conversation pieces. I look around for cheap little things when I'm at thrift stores and antique stores. My favorite so far is these tiny glass ladybugs that I got for $1 each. I keep them in a locket and give them out when I feel like it.
Another tiny gift: I often play a made-up Scotsman I call Tristan Buchanan, so I bought a spool of cheap Buchanan tartan ribbon. I give it to patrons in 18-inch lengths. Sometimes I say to show it to the Queen/King and say that Tristan Buchanan sent them. They love it.
I have a new gimmick this season. I bought small glass bottles with corks at Dollar Tree, 6 for $1, plus tiny alphabet beads, $1 for a bag, and filled the bottles with beads. Occasionally I'll ask a kid their name, then say that I've got that name in a bottle and give them one.
You should not miss the guilds. Guilds, like mine (guildofstmargaretinc.com), are usually putting on a show purely as a hobby. They are there to have fun with each other but even more so with the patrons. They want you to come into their pavilions and talk and play.
When you come up to a guild pavilion, make something up. Have a question, or a joke, or story, or a song, or a dance, or a funny quote. They want to hear it and they want to improv with you. You can ask to be given a quest, you can give the king or queen a gift, ...
In my guild, one of the best recurring bits is the trials. If you want fun, prompt a trial: wear something that will be deemed disloyal (e.g. a Hawaiian shirt) or that will cause you to be accused of theft (like "cathedral glass" e.g. sunglasses) or just make an accusation.
Guild members want to talk to you. They all have names and characters (who might be made-up or historical) and they want to tell you about them. They want to hear yours, too.
Guilds like mine don't charge money. We will usually give you something, like one of these favors, when you come talk to us at the pavilion. The favors are lovingly handmade by the guild members. Some people collect favors and wear them on their garb year after year.
Kids are absolutely welcome and they will definitely get an age-appropriate favor if you bring them to meet the King or Queen. Sometimes we have a little treasure box of toys for kids to dig through. We'll also knight them or send them on a quest or make them a prince/ss.
A lot of guilds will have games out: cards, croquet, giant Jenga, and so on. You are welcome to play with the people you came with, with guild members, or with other people you run into at the faire. There might be games you don't know. Ask and someone will teach you.
If you want a guild to play in some storyline you're trying out at the faire, they're usually flexible about it. If you say, "If someone brings you a piece of Buchanan tartan ribbon, it's stolen from me and please put them on trial for theft," there's a good chance they'll do it.
Faires have bands and shows. Someone else will have to tell you about them because I hardly ever make it to them with all the fun I'm having with the people!
OK, that's all my recommendations. Here are the "don't"s that occurred to me quickly: - Don't touch people or their things without first getting permission.
- Don't make undue assumptions about pronouns. If someone is in Renaissance clothing, which is very gendered, it's usually safe, but many patrons don't wear Ren garb. I usually start out by referring to people as "gentlefolk" and look for pronoun pins and ask if I need to.
- Don't play a historical character that would belong to the faire. If the faire has the court of King James I, don't play King James or Queen Anne or a leading courtier. Play someone you made up, or an ambassador from another country, or anyone else really.
That's all I can think of now. Have fun!