If your website is under performing it may be time to get the experts in. Many developers will create a website that is aesthetically pleasing and functions well but does not have the necessary Search Engine Optimisation to get it to perform well on the search engine results pages.
There are some basic SEO elements that should be implemented on all websites. Often one element on its own is not enough to make that much of a difference but when combined with your other online marketing can move you up quite drastically.
A good web marketing company will be able to assess your current site and tell you what is required to get it up to scratch. They will most probably also recommend ongoing marketing work and this is not just to line their pockets, but it so you can retain and improve on your rankings.
Often SEO work is done in phases and in a specific order so as not to have to revisit a part of it again unless there are large changes to that page or area.