If you're going to build a web site, you obviously want it to do well, for the reason you are building it. Most web sites (though not all) will want visitors, so once you've decided which co-hort of visitors you are aiming at, you need to focus on what information you're going to be passing on to them, this could come in the form of an expertise you feel you specialise in, some goods you want to sell, or something more newslike, something you're going to be constantly researching and updating, or maybe a mixture of these. What's important is you know your subject, and you know where you're going to research the information from.