This is a big one. The design is the most important part of the user experience, although it’s very easy to find successful people on the internet who might argue with me. Craigslist is the best example: no design, no brand, a huge success. But this is rare, don’t think that if Craigslist managed it, you will too. Design for the user and all the time think of how they interact with a website. It might be a good idea to ask the client what kind of clients he has. What kind of people are they, what do they do for a living, how much time they spend on the internet and so on. This is important to consider when designing for the user.