In any business it is vital that you do plenty of market research in to your competitors. You need to be constantly accessing the situation to ensure that you are offering your visitors a reason to use you over and above anyone else.
It may be that you can offer your goods and service at a cheaper price, which will give you an advantage but you need to make sure that you advertise this and that the experience they have when on your website is a good one. You may have a better product or service or be more competitively priced but if your website under performs you may be missing out on a huge number of sales. One stat that you should be aware of is bounce rate. This tells you the number of people that have left your site without interacting with the page. If this number is high then it may be that there is something putting people off your site. For some pages this is ok such as a contact us page where they may just be looking for your phone number but on your home page, this could signal that something is wrong.