We've learned how to be a good commissioner, but how do you run an art shop and bring in the customers? More importantly, how do you keep them coming back? Read and learn, my friends!
The key thing to remember is that art shops boil down to one thing; You are running a business. Therefore, you should treat it like a business. Which means....
Stay professional: You can goof around or be yourself anywhere else on CS, but once you enter your art shop thread, you should be nothing but professional. Address your customers politely, respond to questions, try to alleviate as much stress and concern as you can. That being said, here's how you stay professional.
I. Keep your anger/irritability in check: Nothing scares off customers faster than an angry artist. Snapping at your customers is an absolute no-no. Imagine you walk in and you see this...
User: OMG MAKE ME N ARTZ PICTR!11!!1!
Artist: Jesus Christ you people are thick! Fill out the form and speak English, dummy! Can't you read the freakin' rules?! Why do I put up with this crap?!
Would that response make you go "I want their art!" No! That would make you go "Good God if that's how they act with an inquiring customer, how will they treat me when I enter a business contract with them?" Your attitude in your thread can make or break commissions. I know most people when looking for art, will factor in attitude into the commission equation.
And no, a "bad mood" isn't an excuse. If you're having a bad day and you just can't handle the stress of dealing with customers, just don't do it until you cool down. Nobody will hold it against you.
II. Keep spam to a minimum: You can chat with your fans, but ideally your art thread should be just for ordering art or addressing concerns with your art. The bigger the thread is, the higher the chance of lockage. Plus spam is against the rules.
Moving on to different points.
All play and no work make you a broke artist:: Taking commissions means you make a commitment. You have to make a product, deliver product, and get your payment. That is your commitment. Your commissioners DO NOT pay you to chat with your fans and do absolutely zero work. Don't get me wrong, you can chat with your fans, but budget your time and make sure you get your commissioned art done as well.
Make yourself available: Many users are intimidated by artists for some reason or another. Always have your PM box and thread open for commissioners to ask questions, request changes, inquire about other services, etc. Invite people to take advantage of the fact they can contact you for any reason. Just a note to commissioners; do not abuse that privilege.
Keep your posts tidy and easy to understand: If you have a multi-post thread like I do, reserve the first post as an index to the others so people can skip right to the rules, forms, examples, etc. It's easy to navigate and people won't get lost as opposed to a one post thread where everything is crammed together and confusing to sort through.
SOAPBOX MOMENT- Codewords:: I'm calling this a soapbox moment because this is just a personal pet peeve and several art shop customers have expressed frustration with this system; codewords in rules. It's fine to have a safeguard against people who blow past rules like one rule that says "if you read this, put the eye color of your character at the end of your form."
Codeword puzzles like this...
1. rule
2. Put orange as the codeword
3. rule
4. rule
5. Don't put orange, I'll ignore you. Put banana instead.
6. rule
7. Don't put banana, put apple pie but instead of apple put cherry.
Are irritating and stop people from ordering because they don't want to waste their time playing mind games to get a piece of art.
Keep your customers in the loop.: Having an art block? Say so! Moving or will not have internet access? Add a notice in your shop! Keep your customers updated so they won't be in the dark wondering what you're doing or if they will get their art. It will give them piece of mind and save you the stream of "WHAT ABOUT MY ARTZ" PMs.
Don't be afraid to say no or cancel a commission and refund if you can't do it: If someone comes to you with an absurdly complicated sparkledog, don't be afraid to say no if you don't do complicated characters. Your art shop, your rules. Yes, they are paying, but you have a right to say no to a request, just be sure to be polite about it. At the same time, if you take on more than you can chew and just don't want the stress or something comes up in your life, it's okay to refund the commissioner and explain why you can't do it.
Tris added these two suggestions. (Quotes is what Tris said.)
"Do not resort to begging if you art doesn't sell: "No "please please order, I'm bored" in bump posts. Art on CS is a competitive market, and most people don't seem to make it through.

Advertise wisely: "Do NOT send random people "special offers" from your art shop, and do not mass-PM people asking for business. That's not only a reportable offense, it's also super annoying. In fact, I don't even think you should mention your shop unless someone asks if you have art for sale first. I can't count how many times I've just been having a friendly conversation with someone, then suddenly: "OMG VISITS MAH SHOP PLZ PLZ PLZ". =___=""
This also goes for art contests. Think of it this way; do you like those e-mail spam advertisements clogging up your inbox? All that work deleting 419 scams and drug ads when you could be doing something productive? THAT'S how artists and customers feel when you bomb them with PM spam advertisements. It won't bring in the customers, it will drive them away.
But where do I advertise?: Your signature of course! Your signature is a great place to put a link to your art shop! There are some (now defunct) art shop directories you can post in too.
(Suggested by Moonstar10) Consistent Above Good: Examples are wonderful. They show your customer exactly what they're going to get in terms of quality. Use plenty of examples with different poses, species, types of medium, etc.
Just be careful with one common art shop pitfall; put up the quality of art you feel you can deliver at a consistent rate. Don't show your absolute best piece of art ever as an example because when you do art requests and deliver a piece, your customer will be disappointed when what they get is less in quality than what was promised.
If you have any additions at all, say so!