A natural question which comes to mind when you are already ranked high is: How do I hold on to these rankings…? The answer is simple: Put up more unique content, consistently!
Search engines love content and for a good reason. The internet is a resource of information and websites which provide mundane, old info get phased out.
A good way to provide content is to install a WordPress Blog on your website. Installation and maintenance of blogs is very easy (provided you have at least some technical skills). A lot of people simply do not blog because they do not have the time or cannot pay someone else to write posts for them.
Go ahead and check leading websites which are ranking high for their keywords and you will find that they have these points in common:
1. They have a blog where the management team posts to every day.
2. They have a lot of users, which post a lot of info, such as comments, suggestions, reviews etc.
3. They have a lot of sales and information pages (apart from blog posts) OR
4. They have spent TONS of money in SEO efforts without doing any of the above 3.
Technically, you can rank fairly high by spending a lot on SEO but you should not do that as it is the more expensive way. A CMS like WordPress can easily help you gain rankings in a short period of time.