For me, the 2 biggest issues to consider when building your eCommerce website are Search Engine Optimization (SEO) and Usability. These things are really quite dependent on each other. To build your customer base you need to easily found, but to keep those customers you have to have a site that is easy to use. I always harped on the importance of Web Usability, but having never worked in online retail before, I didn't realize how important SEO was to the success of a site.
Unfortunately I'm not an expert on SEO, so I can't advise on how to improve your existing shop. But I can say that if you're starting from scratch, it's important to interview your hires about their SEO experience. It will only benefit you to make a good hire in this department, even if it costs a little more. What you'll save in monthly advertising expenses will be worth a little more money spent up front. Trust me on this one. I spent months trying to get my fabric found in Google searches, and no matter what I did, it all came back to issues with the coding of the site.
I'm a big fan of usability. There is a fantastic book called "Don't Make Me Think" which basically explains how visitors to your website will spend more time on there if they don't have to think about how to use it. For example, if your customer has to think about how to add something to their shopping cart, they might not make that purchase. If your customer can't find a coordinating print to the one they fell in love with, they may not purchase either. You may have the most visually beautiful website out there, but if it isn't easy to use, you may not make the sales you are looking for.
When designing my shop, I kept going back to all the things I like about other sites I've shopped on, and thought about how I shop for fabric in brick and mortar stores. I love the color wall in quilt shops, so I wanted to make sure that you could sort the fabric by color on my shop. When shopping online it always frustrated me how many clicks it took to add a bunch of fabric to my cart, which resulted in my Quick Shop. It was important to me that you didn't have to go back to your shopping cart every time you added a new fabric - especially with the Quick Shop - so I designed an overlay that opened up to display the cart and then automatically closed.
From the feedback I have received, I think I had a pretty usable website. I never had complaint about how to find something, even though I didn't have a search function, and the only issues that ever came up were because of a glitch with PayPal. My checkout process needed work, but overall in the usability department, I think I was a success.
When designing a shop from scratch, it is important to ask how you think your customers will expect to shop on your site. Don't make assumptions such as 'they'll find it' or 'they'll figure it out' because they won't, or more importantly, they won't want to. There are other shops out there that may be easier to use. Make sure that if you get that customer to your shop, you keep them there and encourage them, through usability, to make their purchase with you.
I have been busy working on a few projects outside of the selling fabric world. One of these is a usability project that I'd love your feedback on. But before I post about it publicly, I want to get permission from the sites owners. Get ready to do some clicking around and note taking. I'm hoping this exercise will gel the importance of having a usable site.