I honestly don't remember, which can be taken as a good thing! Nothing awful happened to leave a bad memory. So it was really just business? I did what they asked, they seemed to be happy with it, doneso!
I suppose the #1 thing to stick to is clear communication. I let the client tell me what they want, I ask any questions if things need clarifying, and then I work on a sketch. To be safe, I like showing the client a sketch first before proceeding with inks and colors, just so we're on the same page. And they can request minor changes at the sketch stage, so it's better than having to undo a lot of coloring and inking work.
As for asking for a commission, I provide references first and foremost, give a general description of what I want, and then let the artist go. Usually with a commission, I give more leeway to the artist since I really like their work and the pieces are just for my own private collection--I'm not using them for any specific purpose that might require more exact instruction.