I always wanted to make a post about this so here goes...

My experience has been somewhat minimal compared to others. I've sold art at Artist Alley for about four years, only six conventions in all.
Anime Detour 4. Anime Iowa 1. Fall Con 1.

Some tips:

-Be nice and polite to everyone or be careful of what you say.

Lastly, there's stories I hear artists at cons who behave rudely get bad rep online and off. So be nice to regular con go-ers. They might talk about you elsewhere.

-You don't have to be the most skilled artist there to get people to buy your stuff.

Creative ideas work such as selling something that no one else has...I've seen plushie fruit, plastic eggs that hatch into fuzzy creatures, plushie heads with censor signs over the mouth...weird gimics that work.
Also if you are willing to go that way, drawing lusty artwork sells. There's a big audience for yaoi and the like at Anime cons. At regular American comic cons drawing beautiful females works too.
Simple art such as chibis sell. Lots of art sells just because the subject is of a popular character.

-Always have easy-to-spot price labels on your art.

People aren't going to ask for the price. First con I sold art, I didn't put on labels and didn't sell anything until I made some.

-Promote your original work.

You can promote your comic, webcomic, novel, website or original characters by giving away business cards and selling related merchandise. Just a note though, selling original characters or comics at Anime Cons isn't that profitable unless your comic is a parity of a popular anime/novel/game or your art is really really good. I've only been to one comic convention, but I think that is more up your alley if you want to sell original comics.

-Be good to your fellow Artist Alley artists.

When it comes to selling your original work, the people most likely to buy them will be your fellow artists of the artist alley. (Maybe because we appreciate small-time art more or maybe because we're in the artist alley longer than the dealers room.)
It is also an opportunity to network with other artists. Make friends. Talk spoilers. Get tips. The like. If there is an artist gathering or dinner after the AA hours go to it.

-Relax at a con.

At every con I've went to there is always ALWAYS stressful situations that pop up. The stress usually comes in the beginning when your rushing to get to the con and on the last day when you are absolutely exhausted.
The big thing is don't let it get you down or make you lose your temper. Making a big fuss ruins your time there and it makes it more stressful for others. Try to set aside at least a few fun or relaxing activities you really want to do at the con and assign someone else to watch the table for a short time.

Questions, added tips, or comments? Please reply.