I have been commissioning artists for longer than I've been on deviantart. In 2009, I wrote a news article called How to Commission an Artist, and I do my best to remember all the experience that went into writing that and to follow my own advice. That said, I can forget that experience or make new mistakes; please forgive me if I err while commissioning you.
Information I'm looking for:
1. What are your prices?
2. Do you use PayPal, or some other method of payment?
3. Do you want to be paid all upfront, all when the art is finished, or half and half?
4. Who has commissioned you in the past, and who is commissioning you now?
5. How long