-Make your product easier to buy than your competition, or you will find your customers buying from them, not you.-Mark Cuban
The design of your site is important. It is like the entrance to a store. When a customer arrives they need to be able to find what they are looking for as quickly as possible. If they cannot they will quickly jump over on to another site.
Think about how often you have done this. You arrive at a web store looking to purchase something and you can not find what you are looking for or if you can you have to jump through countless hops to find a cart and to purchase the item.
Most online business people would suggest that you do not handle this aspect of your business yourself. They would suggest that you spend some money and have another service provide this for you. Yes I know that we live in a diy world. I am a huge fan of do it yourself, but in this case you should have others do it for you. When you are a small store you can do business out of a shoe box or a chase drawer, but as you expand you will purchase a register and then computerize multiple checkouts. That is the progression from store, to big store to department store to franchises.
You need to progress from simple buy it now button to professional checkout.
You also need to update the look and feel of your site as often as possible. If you run a WordPress site take the time to do the updates. It does not hurt and it can only improve the look and accessibility of your site.
If you have not built your first website then I would suggest that you do your research well. That you investigate what has worked for others. Spend time on Youtube and watch some tutorials from the professionals. Take advantage of all the free information you can obtain. Take advantage of all the deals that come your way during any given year. Always look to grow your online presence. Improve your hosting packages. Do keywords and domain name research so that SEO becomes easier. A good name for a website can generate a great deal of organic traffic.