The most important part you should consider when you start to design a site is its target. When I say "consider" I am thinking about 2 important things: the template and the functionality of the site (that's the web designing and web developing part of the web page) and the content adding (after the development is ready and the site is online).
Of course, there is no chance to be taken in consideration if you want a business page and it looks like a child's play (or something very different of what it should suppose to look like), but that can be arranged and it should not be a problem with a good team to do your site.
My subject is now different: what you do with the web page after it is online and you must maintain it (writing content, adding pictures and videos, adding news or everything you consider appropriate). That content must be also targeted: you must always have in mind the main subject (or subjects) of the site. One of my clients was selling women makeup products and his content was very poor, it was not developed in the last few months (since the web page was put on server). All the data it contains are the list of the products and a very short description (some of them with only a few words). I advice them to write about the makeup products, and they can approach the subject about how to apply the makeup or why one product is better than others or why should do one thing instead other. That never happen (the writing part), at least not yet, but all of these are good subjects for developing the seo for a targeted site.
One of my recent clients is a foundation that has a shelter for elder people near Oradea (Romania), their site is dedicated to present that shelter and their services online. In this case the target is not only the building itself (with pictures and videos) and the inhabitants (in the case they want to appear on the page), but also the surrounding area (and some words about the history of the place) and all the events that will happen and that will be related with their activity.
Never forget that the target of your site is strictly related with your activities and all the data you add on it should be around that. It depends only to you to decide how many targets you have on one site, but my advice is to keep as few as you can. If you do too many it might happen to fail in doing them right. Remember that you can always extend your activities when some of your current ones are finished.
When designing and writing content for a dedicated page (for a business or a specific activity) it is rather easy to find targets and subjects to write about. But if you are not sure about your target audience you have several options to find information about:
The network of people around you. I mean your friend, your family, your co-workers and acquaintances, they can always give you advice and they can tell you what they want and what they are searching about.
Research in the real life and online. In time you can always tell what are the trends in some fields of activity, but you can also have a lot of places you can found more and complete your information about what you need to know.
Join the discussion groups. It's important to know what the people are talking about, there are a lot of good ideas there.
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