Your blog — if you have one — is a great tool for improving your search engine rankings in Google. Google loves fresh content and your blog is the best way of adding fresh and unique content to your blog.
The problem with a normal website is that you can add only a certain number of pages. Most websites have at the most 20 odd pages. But if you incorporate a blog into your website, you can have new blog posts almost every day, and this gives reason to Google crawlers to visit your website on a daily basis. Newer blog posts also mean there are more links that can be indexed and ranked.
While writing your blog posts you should focus on creating keyword rich content. Read here how to search engine optimize your WordPress blog. When you repeatedly write content based on your niche keywords it increases your keyword density and this gives an impression to Google that yours is a specialized blog. Marginally improved Google rankings may create a cascading effect as more and more people can easily find and link and promote your content.
High quality content also encourages other webmasters and bloggers to link to your blog and this helps you garners incoming links. Read more on this link.