This is a big, big topic. But, in the interest of posting and not taking all night typing, do think about these areas when you're working on it.
1. Design: The basics of how the page is laid out, color palette, how the look of the site reflects your company's brand, how it will look to a prospect, and how the information on the site is presented (navigation, text, printability, etc.). How each of these factors comes into play is determined by your company's brand, services/products, target audience, online goals, online lead generation strategy, and probably a bunch of other factors that I'm not thinking of at this second.
2. Content: Everything from page names to headlines, and the actual text of your site to SEO. The content is a very very important part of your website – so make sure you don't overlook it in the frenzy of designing and coding your site.
3. Functionality: What's your site's job? If you had to choose one or two things for your site to do for you beyond the very basics of getting found on the search engines and giving basic information to your customers and prospects, what would that job be? Growing a mailing list? Selling a product? Selling services? Getting media attention? Something else entirely? I suggest that a business just starting their website not drive themselves up the wall by trying to split their focus and concentrate on too many website functions at once – build the site to do the basics, then add on a functionality or two at a time in rounds of revision. That way, you'll have realistic amounts of work to do to get your site up and live – and then you can come back and tweak it over time. And once you see how it's actually working for you, and once you get customer feedback.
4. Managability: You want your site to be something that you can work on and with over the years. Ideally, your design, content and functionality will all be coded and set up in a way that you can get in there and mess around with it. This is really important for testing/ modifying the site over time as well as for SEO, and just for the general purpose of keeping the site updated and current. Whether you build the site in WordPress, or even just code an HTML site and pick some easy-to-use website updating program like Adobe Contribute – it doesn't really matter – as long as you can get in there and edit your site.