You find someone that you think would be interested in buying your art and try to convince them to purchase from you. If the say yes, start on the project, and if they say no, learn from that experience, and move on to the next person.
Prior to having a customer, you don't really need to worry about payment. And getting that first customer is often an uphill battle.
Over the internet most people use paypal for payments.
Most people who do commissions get details of what the customers wants and submit a rough sketch or two of the in progress, and have a point after which no changes are allowed.
G-SketchFeatured By OwnerDec 5, 2012Student General Artist
For doing them online, defiantly go with PayPal. If you are under 18 have a parent create an account in their name and use it. This is VERY important because you don't want to end up with a locked account for being underaged. You will not be able to get any money you might have and your commission sales will be busted. (this happened to me and I'm just now getting back into selling commissions )
Also VERY important. ALWAYS demand half the money you are charging BEFORE you ever start working on a commission. It never happened to me, but sometimes people never pay you after your work is done and Deviant Art is not responsible for that.
Have an informations page set up. Show examples of your work and list prices. Also give some more information in the description to give people a better understanding on what you're all about.
(this is something I did and one someone els I know did ) Then promote, promote, promote! Get the word out! Go to the Job Search forum and see who needs a great artist like you!
Firstly you need to make sure you have the kind of art online that you're willing to sell, so that you have a portfolio that says "this is what I do" because no one will hire you if they don't know the sort of work you do. I'm assuming you post on dA so you'll have a selection of works showing this off.
Secondly you just make it known you're doing it. A journal, in your dA sig, anywhere else you post in your sig, perhaps put up a price list of things you'll make and how much it'll cost.
Paypal is the best way to go for pay, you don't have to give out your bank details to random strangers then as it's all done via email adresses.
If you do traditional make sure your customer will get a very high quality scan or photo, because no one wants to pay money for a bad scan.
In the mean time just keep drawing, keep producing better work etc so you're constantly improving what you do and making yourself more attractive to buy from.