Having fresh content on your website is vital. The search engines like to see that you are offering your customers up to date information and that your website is not stale (not changing for months / years at a time).
Not only do you need to add fresh content to your website but this content needs to be relevant and unique. You cannot just copy and paste an article from the BBC for example as this can be classed as duplicate content and therefore will be ignored or even get your site blacklisted.
A great way to add new content to your site without cluttering up the design is to add a blog. A blog will allow you to write news articles / useful information on a regular basis, but keeping it out of your main content for the pages that are most important from a user’s point of view.