Focus On Your Target Audience When You Design a New Website
Ideally your website should be designed in a manner which is appealing, both in terms of visual appearance and the way that content is presented, to your main target audience, the type of people which makes up the bulk of your sales.
Obviously some businesses will have an easier time achieving this than others , for example, the demographic of a general store will be extremely varied whereas, by comparison, the target demographic for a builders merchant will largely be people working in skilled trades and enthusiastic DIYers - far more specific and targetble.
If you have a firm grasp of your target audience then try and create a website which advertises your products and services to them in the most appealing and digestible manner.
If your business is quite varied then it's typically best to keep things simple, both in terms of web design and the way in which your content is presented. A storefront, for example, should display and categorise products in an intuitive manner so that they can be found easily when searched for.
Additionally, a technical services business should know that their customers will be largely laymen so the use of basic explanations and frequently asked questions can be used to provide the customer with confidence and help overcome potential barriers to sales, or at least make the process of arriving at a sale more efficient.
Another important pitfall to avoid is the use of mixed messages. Referring loosely to the example from the above paragraph, it would be of no use if the home page of a mechanical engineer tried to appeal equally to people with an engineering background and laymen at the same time - although a bit extreme think about if one paragraph provided simple explanations whilst the next was highly technical and scientific; all this will achieve is to put everyone off. If you really feel the need to appeal to both ends of the spectrum consider separating the information onto different pages and market them appropriately.
Likewise don't try and appeal to commercial or corporate clients and local people alike by taking a cake decorating approach. By this i mean don't create a website with the intention of appealing to a specific audience and then simply adding decoration (think random page elements, pictures and caricatures, for example) with the hope of attracting members from another. Firstly, this is unlikely to work (the problem of mixed messages once again) and, secondly, in doing so you will typically diminish the aspects of your site which were designed to appeal to your true demographic in the first place.
As I've said above, if you do indeed wish to target a varied and broad target audience then your website will have to be fairly generic in design and presentation. Better that then creating a conflict which could ultimately harm your ability to appeal to any customers at all.