In order to make an effective website there are many different elements involved. You need to decide who your audience will be. If you don't know who your audience is there is no way for you to direct the content and style of your site to fit their needs, and will lack the structure necessary for it to be an effective website. Your website should have a visual theme, and should not look like a mosaic of different elements haphazardly put together. Unless of course this would be appealing to your audience. The information on your site should be broken into manageable pieces, similar to the way you give your students pieces of information one at a time as you go through a unit. Links should work, and be provided for navigation within your site, so the back browser button is not needed to return to a different page or the home page. And lastly, each page should be designed, there should not be pages left unfinished, or unorganized with elements missing.
It's also important to keep in mind what people are looking at when they evaluate your site. Who is the person behind the site? What is the site about, and is it useable? When was the site created and last updated? Where is all this stuff coming from? Why am I looking here for this information and not somewhere else? If you have all the elements above, and you do not fail when you ask yourself the questions people are asking about your site, then you are on your way to a great website!