When you create a website it needs to cover different areas. The first thing it needs to be is easy on the eye. It needs to look good and easy to ready and work around the site.
The themes and colors should match the niche you are in.
If you use audio or video on the pages do not, yes do not have them start as soon as the page opens, have the person start them. The reason for this is if you are looking at a site in an office or somewhere the last thing you want is a loud noise suddenly start.
Use good keywords on the site.
Yes SEO is a must, but I believe you should always design a site for your users and SEO falls into second place