There are a lot. But start with guidelines provided by search engines. All other things are secondary.
For better SEO use meta tags, have a permanent redirect either with www or without www, provide a feedback form. If you are having a blog then make sure that you include the blog feed url in the head tag. That way the search engine can easily index your pages. Use better keywords. Suppose you are writing an article and you are confused with what keywords will be used for searching your article you can use freekeywords dot wordtracker dot com to check out the number of daily searches for a particular keyword. These are a few tips. There are many more that can be added to this list.
SEO is something that updates almost everyday as search engine updates their algorithm. There are a lot of aspect in terms of SEO. I suggest you to read the Basic SEO PDF ebook from Google. The rest you can learn from DP forum.