They say rules are made to be broken, and as soon as I post this list, someone will be able to point out a website that does not have one or more of these features on the easily accessible wildly successful, anyway. But GENERALLY, there are some things that visitors and readers expect to be easy to find.
Incorporating these elements into your design may seem obvious, but it's amazing how many sites I visit that have not remembered to include them. Nothing irritates me more than to read a great post, and want to find out more about the author's credentials, only to have to search all over the website until I lose interest, trying to find an "about" page. Also, I as I'm reading, I often think of a resource I would like to share with the author - but end up not being able to it, because I can't find the "contact" information.
Planning is important. Even if you incorporate these elements, but move them around every other week, your regular readers might become annoyed. I have one credit card company that I pay online. Every single month I have to search for the "pay your credit card" link, which is moved around and re-named - every month. It's quite exasperating. I think they may be doing this on purpose, to try to keep people on the site longer, hoping we'll be distracted by all of the good deals, but it doesn't work for me. I just find it irritating. Moving things around is sometimes necessary, but it's usually a good idea to maintain a relatively consistent "look" and "feel," to your site, and to make your most important features as easy to locate as possible.
Also, it is important to include these most important features in the header, sidebar, or footer of your site. If you have them only on the front page, or on a splash page, visitors who enter the site through a link to a post will have a hard time locating them. So, what do you absolutely need to have on every page of your website or blog?
An "About" page. It should be called that, because people will use their browser search bar to look for that term if the link isn't easy to find. In a world where anyone can write anything on the web, your readers will want to know who you are, and what your authority is on the topic you're writing about. If you have a local business, they'll want to be able to read a little bit about the history and philosophy of your business. This is an excellent opportunity to make a personal connection with your readers and/or potential clients.
A "Contact" page. Again, it needs to be called exactly that. Whether you get all fancy, and include a contact form (WebRev's Tim Short knows how to do that for Web Revelation customers), or just simply want to put a simple page up with your name, e-mail address, ph#, and business address (never use your home address) - you need to have a way for people to contact you about your site. In some cases, they may want to alert you to problems with the site, or ask you questions. They may want to share resources with you. Yes, some will spam you, but that's the price you pay for being online, unfortunately. Tim Short does have a way to configure that contact form of his to require people to use a verified e-mail address, so if you're getting a lot of spam or other unpleasant mail through the contact page of your site, be sure to talk to him about that. If you are a local business, you will also want to include directions (preferably a map) to your establishment. This can be done through any online mapping service like Mapquest, or Google Maps.
A "Home" Link. Not only is this really good for search engine page rank and site mapping, it is important for visitors who entered your site through a link they found on a social network or that they got from a friend or press release. Once again, this link really needs to be called "home."
A List of your Most Important Pages and Links. Now this list can have various names, depending on what is appropriate for your business, your industry, your site, and your personality. It might be your menu if you're running a restaurant. It might be a list of your pillar posts (most linked-to) if your site is writing-intensive. It might be a list of industry-specific health resources if you're a doctor's office. You get the idea. Whatever people are going to visit your site to see - make sure they can easily find it from every page of your site.
A "Payment" Link. Again, this link might have different names, depending on your business. It may be a "checkout" link, if you have incorporated shopping-care technology on your site. It may be a "donation" page if you are a non-profit. Whatever you call it, make sure it's easy to find.
Can you think of any other must-have resources for a website? Please share!