Many companies spend a lot of time planning out how their website will look and function but then forget the importance of the content. As a web designer, I all too often get asked to fill in the content section of a site for a client without them really wanting any input in to it.
When writing content for a website you should consider what message you want to get across and make sure that each page is specifically related to that service or product that you are wanting to promote. Content writing is a balance between writing purely for the customer and writing for search engine optimisation purposes. Good content should do both equally.
Remember to consider keywords, keyword density, call to actions, internal links and also ease of reading i.e. fonts, size of font etc.
If you know what you want to say on your website but have little or no experience and knowledge of SEO then I would suggest working together with someone that does to make sure that you get the right balance of both.