Do not make your site full of graphics. It might look nice but if your page loads longer than 10 seconds it’s a great way to discourage and loose your visitors. Not everybody have cable internet connection and a lot of people are using mobile connection to browse. The more kB to download the less visitors you have. Less visitors is less customers.
Content of your website has to be easy to understand. You have to adjust the content to every possible visitor who might become your customer.
Confused visitors trying to find basic information is another good way to discourage them. Website navigation has to be very simple and easy to understand. Contact information should be easy to find in one click. Consistency of navigation through your website is also crucial.
Flashy distractions are killing your content by distracting the reader. It might be tempting to bring in some cash by putting banners and affiliate programs but don’t do this. Some of your visitors will be annoyed and leave. Other will get interested in the ad and click out of your website. Both situations lead to loosing and giving away customers.
Do not spam to advertise. This way you will get bad reviews on forums and online communities among your possible customers. Use the social media and all other forms of communication via internet to advertise your website wisely. All of that can be done free of charge all around the web.