Web users don't read your carefully crafted web pages, they scan them. So it doesn't matter if you have explained what to do in detail: if the right thing to do doesn't leap out of the page, users will do the wrong thing, click the wrong link, search in the wrong box, select the wrong option. Your job, as a web designer, is to make them do the right thing without them having to think about it.
Steve Krug's short, readable book gives lots of good advice on how to do this: how to be consistent, how to design a page without clutter, how to place things on the page where people unthinkingly expect to find them. (It assumes you are building a commercial web site where you want to provide a service to your customers, but much of the advice is generic.) The book itself is a nice piece of design, itself well-written and uncluttered. It has little that is startlingly novel, but it is well-expressed, and has the key points in one place in a nice digestible chunk. And the chapter "Usability Testing on 10 Cents a Day" should be adhered to by all.