Step Three, The Art
There's lots of artists out there. People who are capable of drawing a lot of amazing things in different styles. By now you should know what the three basic types of art in B/C shops are.
Pixel, Lined/Templated, and Unique art.
There are pros and cons to each.
Pixel
Pros: Easy to sell lots, fast at a cheap price. Often times not color-intensive, breeding intensive or anything like that. Lots of pets that can move fast and are easy to make. Small pets with cute faces/concepts and frequently customizable certs.
Cons: Cheap as dirt. In general nobody wants to pay more then a thousand on one with nothing in the cage. Lots of boring cert work, putting stock items in cages, on certs, and stock pets. Big order forms and requires high organizational skills. Small pets, too small to be fun artistically. Fixing those things with a more complex pet like Matope can be hard to color and harder to edit.
Lined/Templated
Pros: Common and LOTS of good artists around for this sort of pet. Very popular and allows for a more intense quality and environment. Lots of edit options and significant artistic freedom. A very recognizable set of images. (Everyone knows where that pet comes from.)
Cons: Perhaps too popular and a bit over-used? Lots of shops like this flooding everywhere. Lines and shading must be pretty exceptional to stand out. Certing is a bigger hassle on your artists who just want to color, edit and have fun. May require hiring a dedicated cerist.
Unique Art
Pros: Pictures are completely custom for the customer. Nobody gets the same thing twice and customizing a pet is not nearly as hard. Can have a stronger loyalty base for a particular art style featured there and LOTS of flexibility to do whatever you please with it.
Cons: Not very economical. Pets require much more work and can be very expensive, which goes to any artists you hire, not the shop owner. As such the shop owner has to have good art skills to get much out of it. Needs a much stronger shop concept then most places to ground to artwork in familiarity and if there is more than one artist their styles should generally match in concept. (Example, can't have one person doing chibis, another doing painting styles for the same stage of a pet.)
Look at various shops around the B/C to see what they're doing with their shops. Some big names to check out for each type would be Squeak! Pixel rodents, Soquilli and Edelsteine, but look in more than one. Every shop is different.
Step Four, The Artist
This is also very important. A creative, accurate and unique art style is imperative for a good shop. It can be very hard to find good art at the right price, but there are a few places you can look around.
The main
Breedable and Changing Pets forum has line art auctions floating around here and there. Those are when an artist sketches up a lineart set of their choice and sells them off. There are some very creative things and some very common things in those auctions and you may find something the inspires you or is what you're looking for.
You may also want to check out the
Line Art Auction Directory but keep in mind it is not always complete and can be out of date at times.
You can also go looking around in the standard
Art Shops for an art shop that would sell you what you are after or post a request thread for the art you are looking for
here.
Lastly, you can find an artist that you like very much who has made B/C pets before and send a polite PM explaining that you would very much like to commission some art if they are available. Many of them won't be willing or may not even be on Gaia any more. So be polite and accepting when doing this. You don't want to come across as annoying or tick off the artist you're trying to request art from.
Keep in mind when buying lines that good lines ARE expensive! VERY expensive! I have seen line art auctions go over 10 million before and most go between 500K and 2 million. And that is without shading templates. Be prepared to pay a fairly large chunk of change for good art, and even more if you're looking for lots of stages.