1) Have your website and business materials match the vibe of your product. If you don't want to come across as a small crafter, make sure your business cards and website don't look too "hand made", unless that is a big selling point of your product. Try to keep things clean and simple, people just want to know about your product and you.
2) Represent your product well. Good photography is KEY. Clear pictures (and descriptions) go a long way to help someone make a purchase. Invest in a good camera or scanner, plus a photo editing program, to help you do this.
3) Communicate. That is, make sure your contact information and site information are easily found on your website. People want to know your shipping charges, your return policy, and about where you are located and who you are!
4) Don't have too many ad banners/etc. People may differ with me on this, but I don't put any google ads or ad banners on my website. I think it helps it look more professional and less "home spun."
5) Include any press you may have had in a section on your website. Only put the pieces that are noteworthy (or make 'em sound noteworthy!). A review from your Mom doesn't count! ;-)