The thing about traffic from the search engines is it's free, which is great, and it also has a tendency to convert very well to offers. The sad statistic is that a lot of marketers operate on either very little SEO knowledge, or what they do know is often incorrect. They're so excited about getting started with their business that they do not take the time to learn what needs to be done. The unfortunate aspect is that this will always lead to problems, so we'll discuss these so you will not have those problems.
Here's one that is being seen less, but still done, and that's creating flash websites. They aim to impress their visitors with the amazing special effects that come with flash. But along the way, they forget that flash is the biggest enemy of SEO. It's really a simple, but huge, problem because Flash can not be read by search engine spiders. The simple solution is to avoid using Flash, and you can use just about anything else such as HTML, or CSS. If you just stay away from Flash, then you'll be able to seriously optimize your site for SEO and give it a good shot.
Failing to get the most advantage in terms of SEO has to do with your URL, or domain name. Dynamic URLs can still get ranked in the SERPs, but it's really inexcusable for failing to consider your SEO when you register a domain name. Ok, what you'll use is secondary keywords in your site filename extensions, and then put your primary keyword / phrase in your domain name, or URL. This approach is easy to do and will greatly add ranking weight to your site in the major search engines.