Creating new content is great for SEO
Add new content is great for SEO
Keeping content fresh
You could keep content fresh for SEO by either making small amendments to existing content, or you could add more pages and articles. You could talk about industry news, or any new product launch, or snippets of information you just picked up from other sources. The important thing is to keep adding content regularly.
When you add content you need to beware that search engines do not like duplicate content. You cannot simply add content to your site by copying it from somewhere else. First of all you are in break of copyright law, and secondly this will not help your search engine ranking.
Search engines always store the original source of content, and attribute worth to this. Any copy is either ignored or does not add any value to your site. If you add articles from other sources usually you need to provide a backlink, which is actually worse for your site and dilutes your PageRank.
Add content through a blog
Blogs are a great way to add content to your site. The important think is to have a good content management system that is seo friendly, so that you can manage the title, headers, metatags and url structure. There is no point in starting a new blog and then to stop updating it after a few weeks. Both your visitors and search engines will not like this.
Some sites provide online FAQs. These are great ways to start interacting with your potential customers, and at the same time to add fresh content to your site.