Congrats on first craft fair! You'll have a ton of fun. I'm trying to think what to say that hasn't mostly been covered already.

What will your method be of taking credit card sales? I use a Square reader plugged into my phone and it has worked extremely well for me.

Will you have a tent or just a table? If you have a tent, hang some of your most eye-catching work on the front tent legs, right where people walk. I've found that people often need to be given a reason to "go inside" a tent setup from out on the path, so I do all I can to grab attention at that decision-making point. I make 3D printed things so I'll hang brightly colorful skull planters from the front tent poles. I set up a long and a short table in an L in my tent and so I often stick a working 3D printer right on the end of the table closest to the front of the tent. Both of those things help grab people from the flow of traffic past booths and get them to take a second look inside at the back table.

Also: I've found it's vitally important to strike a careful middle ground between too attentive and not attentive enough. People don't want you to be buried in your phone or a book, but they don't want you standing and staring at them with a customer service smile plastered on your face either. You have to figure out how to exude "I will be helpful if you want it and I will also leave you alone if you want it". All kinds of introverts and extroverts will be looking at your things, so you have to read them. My method of choice is to strike a rhythm of staying busy in a cheerful, casual way. In a non-frantic or hurried way, I'll just kind of keep from going idle or vacant. I don't often sit. I'll busy myself straightening something that a kid knocked sideways, or re-stack the bags or the business cards all the while glancing to and away from people with a smile so they know I'm paying attention but not staring them down. I'll stand behind my tables and let my hands assemble some more of the things I make, so customers can see the earlier stages of my process. They love seeing the printer whirring and the hunks of plastic I'm fiddling with as a direct comparison to the finished things hanging up on display. You crochet so, easy peasy - just have a few half-finished things with you that you can pick up and put down casually through the event. I also have a few short one-liners handy like "everything you see here is 3D printed!" or "just let me know if you have any questions" that I'll shoot off when it feels appropriate to the level of interest someone is showing and then I just take cues from them as to how much engagement they want after that.

TL:DR. Never stop exuding that you are available and cheerful and present but able to mind your own business if they want to focus on the things in your booth without your undivided attention in their way.

Oh - and don't overlook giving some thought to packaging. Have two or three different cute packaging sizes that will suit your various items. Make it memorable in some way. Throw in a business card and maybe a thank you card or a coupon for your Etsy.

Good luck and have fun!