It does depend a bit on type of show/con... Art Gallery show, outdoor/indoor show, fandom convention... all changes what you bring a little.

1. What snags did you run into?
-Fandom/indoor shows: advertising! I am the worst at networking, and making my display stand out and be noted. So, if I happen to be between two larger set-ups, I get "lost" and notice people walk by, distracted by the larger displays
-Outdoor shows: Sort of similar. I am working to make by booth more colorful and attractive to people. Using a bit of psychology by putting smaller pieces toward the back, so people have to walk in to see them (but around a larger piece that draws them in!)

2. What marketing materials worked for you?
I have really only used business cards as material. Socially, I am on as many art sites as I can, plus have Facebook and Twitter accounts where I share my art and announce conventions and shows.

3. Best experience? Worst experience? 
Best: Local outdoor show is run by artists. So they hire people to help with set up and take down of EZ-ups and displays, plus have people that will booth-sit for bathroom breaks, PLUS have lunch brought to you. Some fandom conventions do have a runner for lunches as well, and that makes it much nicer.
Worst: No one event sticks out, but in general disorganization hurts. I like to get set-up with plenty of time, so delayed access to rooms or sites means just sitting on my thumbs. Hate that In similar vein, last-minute schedules of when set-up will be, or even what times the area is open to the public.

4. Did you have Paypal or Square card swipe? Both?
Square. I started with square and have had not problems with it, so continue with it.

5. Did you advertise anywhere like on Social Media that you where going to be at a certain event?
Facebook and Twitter. I have a FB for my artwork, but I do mention events on my personal page as well.

6. What forms do you need to sell your artwork? Any special licenses you need?
Tax license. Moderately annoying as each state has a different system, so getting to know what each state requires can have an influence on which events I want to do. Some states are too complicated for my taste. So far, Michigan, Illinois and Washington are my favorites as they are relatively simple.

7. What is a reasonable amount to pay for a booth?
Depends on the venue. Smaller events = lower cost (since there will be fewer people to make up the cost via sales). Generally, $75-150 is reasonable for a moderate venue. Expect to pay a little more for an indoor venue (esp. if in a hotel, as room payment is expected) and a little less for outdoor.

8. Did you do anything special for your booth? Decorations? Special lighting? Recommended places to purchase booth decorations?
No lighting, as electricity isn't always available. I do try to keep it "open".
Indoors: taller panels on the sides to bring attention. I hang my banner on the front of my booth (though considering a smaller, lighter banner I hang hang above on rods).
Outdoor: I use collapsible bamboo panels to hang my art. Compact for transport and storage, fairly durable, but cheap to replace if needed. However, does make it fairly bland. This year, I am buying some loose strips of light fabric to put between the bamboo panels, both to hide the edges of the panels and to draw interest with color.

9. PRINTS - Do you print locally? Do you order them online? If so, where?
I have an Epson R1900 printer that is a workhorse, so I do my own prints. Usually Matte, but it has the ability to do gloss prints. I tried a small local printer (I am in a very small town) an the quality just wasn't there.