Some great tips have been given, but here are some more!
General:
- Get a card reader from Square or Paypal so you can take cards. It hooks into the headphone jack of your phone. (I have Paypal, but I've heard equally good things about Square. If you have any questions on setup let me know)
- Bring a coat or hoodie, they usually jack up the AC in the vendors hall to accommodate all the people.
- Bring water, snacks, and simple lunches if possible. Pick things that won't leave residue on your fingers.
- Get clear bags for your prints! It sucks to hand a bare print over to the customer without any protection. I recently just invested in some backing board, too, which is nice but probably not necessary for your first con. You can get them on clearbags.com or uline.com
- Keep inventory and a record of your sales each day
Display:
- Vertical is a must! If all your art is flat on your table no one walking by will see it. A lot of people start with wire cubes. I got mine at Target, but I know there are other places. You can also use PVC pipes or a backdrop stand to make a display behind your table, but I wouldn't recommend it unless you have a lot of different prints or you want to hang a vinyl banner behind you.
- Check out your local business supply store. They usually have some tabletop displays available.
- Get little table top easels to prop up your book, at least
- Print out your prices and display them in multiple places. (People will still ask how much something is though...)
- You need business cards! A lot of people take them when they want to check out the art later but can't buy anything. I get mine cheap at gotprint.com. I wouldn't do more than 250 in case you want to change the design sooner rather than later.
- If you can afford it, get a vinyl banner or a banner stand that says your name/alias/studio name. Having consistent branding helps a lot.
Social:
- Say hi to people walking by! If they stop to look, ask them how their day/the con is going. Compliment them on their cosplays, especially if it's one you know. If they comment on a series or print you're selling, engage and chat with them about it!
-Whatever you do, don't look down at your lap constantly while drawing/on your phone/playing a DS/whatever. It really puts people off.
- Don't be pushy, but if they seem interested in particular merchandise (like your comic) feel free to explain it and mention the price. I also have a little folded piece of cardstock that says "Check out our ORIGINAL comic", it tends to catch people's eye. A lot of people like supporting indie creators these days.
- Practice your comic pitch before your event. Make it as efficient as possible, in 2-3 sentences if you can manage. Look up "elevator pitch" if you need tips. LOTS of people will ask what its about, even if you do have a summary on the back.
Hope that helps!