When they want a new design, most folks list "clean and simple" as a priority for the end result. It's a good thing, but much more complex and tricky to achieve than it may seem: you have to accomplish the exercise of identifying what's critical and not exclude important detail. In short, strategy and organization allow for effective simplicity.
Albert Einstein said, "Make things as simple as possible, and no simpler." Edward Tufte says, "For clarity, add detail."
When it comes to visual presentation, these two amazing thinkers are saying that simplicity isn't defined by a lack of information, it means displaying it in a concentrated and focused way. Showing only, and all, the relevant information at the right time is the key to this approach.
Often in the field of web design, we talk about things like "user-friendly" and "intuitive." These terms directly relate to the desire for clean and simple design, as they give people a positive experience with your online presence and generate satisfaction with your brand. If your website is well-organized and users can easily get to the information they need, you instill trust and confidence in your brand.