No patience
Getting visitors to your website is an extremely long process. It can take months or even years before you see any good traffic from search engines. It also takes a very long time to get your visitors to start bookmarking your site or telling their friends about your site. When starting a website, be prepared for the long haul. Otherwise, you might as well not even start because you will only be disappointed.

Not search engine optimized
Search engines are the number one source of free visitors on the internet and are something that everyone needs to take advantage of. Read my 5 basic SEO tips for a better understanding.

No good content
Why do your users even bother to visit your site? You should worry about providing value for your users. Strive for more “quality over quantity.” After all, just because you put something up on your site that takes up space does not mean that people will like it. So, if you find yourself putting stuff up just for the sake of putting stuff up, stop.

Another thing to know about content is that it does not even need to be unique (however, keep in mind duplicate content penalties). Many sites are successful with non-unique content (i.e. most news sites).

Not user friendly
If you have too many pop-ups, lousy navigation, slow loading time, a bad page design, etc you will lose visitors before they even start to view your content. Make sure you keep everything user friendly. Otherwise, why would they ever come back?

Not enough link exchanges
Linking with related sites is the fastest way to build up credibility in Google. Keep linking and linking and you will see your search engine rank slowly begin to crawl up. On the other hand, if you don’t exchange links with others, Google will have no way of “finding” you, and you will therefore be buried at the bottom of search results forever. Check out this post for some good link exchanging ideas.