Everyone seems certain that it's a good thing for an author to have a website these days - but what makes the difference between the kind of site that delivers value and a site that's a waste of web space or full of trash?
#1 - Keep up to date. It seems obvious, but it's so easy to let it drift. A good example of what not to do is John Gribbin's page - it says it's in hibernation, that he's too busy to update it. That's not a great message for readers. But equally it can be just that little detail. As well as checking the obvious spots like the home page, it's a good idea to go through the whole thing occasionally. You can make it less of a problem by trying not to make statements like 'my latest book X' anywhere other than the home page. Then, when you've got book Y out, the page doesn't sneakily go out of date.
#2 - Give them some news. Make sure your home page includes your latest book and some bits of news that change quite regularly. On my own site, I've a news section with just two headlines. Keep it short and sharp, not piles of text. They can always click through to find out more. If you've written more than one book, make sure there are details of all of them. And include links to buy them from an online store - this isn't being pushy, it's giving people the chance to buy, if they want to.
#3 - Tell them something about yourself. I've seen author sites that are great on the book, but just don't give anything about the author. You may feel that it's showing off to include photos of yourself or your biography - but readers can be genuinely interested. If there's nothing there, they will feel less connection with you. And that means less interest in your next book. Take a look at Amanda Lees' neat information page. As well as a biography and my blog, on my 'Meet Brian' page I've included a little interview. Get a friend to ask you some questions (it can be by email if you don't fancy doing this face to face) and think up some answers. It all adds to the richness of the page. Lots of people won't read it, but you don't want your site to look thin and lacking content.
#4 - Include your blog. This is a quick way to make sure your site has up-to-date information. You could, like M. G. Harris, make your author site an enhanced blog. What, you don't blog? Consider it. It's a low effort way to keep a flow of communication with your readers.
#5 - Make it interactive. Received wisdom has it that this is the way to get people involved. At the most basic you can have a mechanism for getting in touch, a way that visitors can email. At the other extreme, you could set up a discussion forum for your fans. This is only likely to be worthwhile if you are already reasonably popular, or aiming at an audience where this works particularly well, like the youth audience. It means a lot of work, if you want to monitor it and avoid nasty material appearing on your site. You may, like this site for Michelle Paver, like to split the interactivity off into a site dedicated to your books. For many authors, it may realistically be a waste of time. The point of having a discussion forum is that it will keep bringing people back - but most author sites are one-time visits, and no amount of interactivity will make people return.
#6 - (Bonus) make it look as attractive as you can. We can't all be designers, but if you are going to bother with a website, make it look inviting. Otherwise, what's the point?