For your original character, it's good to bring a typewritten description of your character, and maybe some words about what kind of picture you want. If you're really specific about the look of your character or you want a more obscure anime or manga character, bring a photocopy of a previous drawing of your character. (It's good to have multiple copies if you want several artists at a con to draw for you at once). The advantage of this is that most artists will otherwise forget what customer #8 on his commission list wanted, having to switch mental gears from drawing to drawing.

Only have one sketchbook? Then get a three ring binder with sheet protectors for putting commissions in. That way you can get commissions from several people at once without worrying about who has your sketchbook. A well-prepared artist will already have Bristol board sheets to draw for folks without sketchbooks. A super-prepared artist might have a folder to put the free page in too.

Don't be too specific on the details of a pose, or it might make the work more tedious for the artist. Artists like to feel like they're creating something from their imagination when they draw, not acting as a tool for the customer.

You also don't want be too general on what you want, unless you trust the artist. If you think an artist can read your mind, you're wrong. If you leave something up to the imagination of the artist, don't be disappointed if you don't get what you wanted. You might get something good or funny though, so it's worth a try sometimes.

No cutseys! If you didn't sign up on the artist's list, you can't get a quickie sketch or a freebie, (or a freebie in a friend's book) without cutting in front of someone that signed up. It's not fair to the paying guys following the rules. I've done quickie pics for folks, but I feel tremendously guilty if the present customer in line floats by and realizes that I'm not working on his drawing.

Be patient and considerate! Hundreds of people go to cons. Lots of people only get to socialize with con friends once a year. People come by and distract their favorite artists all the time, making it difficult to finish the work when it was estimated to be done. Lately, I've had to retreat back to my hotel room in order to get commissions done. It sucks having to hide. Ask the neighbors of the artist's table if you really need to know where he went, since they might have agreed to help watch his table.

Don't ask "How do you draw?" An artist's skill is shaped by personal experience and years of tedious training, and practicing from books. There's no quick way an artist can help you draw better, especially at a convention full of distractions. Every artist has had to draw thousands upon thousands of crappy drawings, and learn from mistakes and remember helpful feedback in order to get better.

Don't bring your life's work to show the artist. If you want an artist to take a look at some of your stuff, it should be a couple of pieces that you feel most confident about. If you have a really full sketchbook, have post-it notes on pages you want to flip to. Maybe 3 or 4 tops. The artist is probably stressed over his workload and the paying customers passing by frequently. There's only so many hours in a weekend.

Take care and have a healthy and happy art commissioning experience!