The most important skill I have learned as a UX Designer is to be able to question what the user will see. Learn to ask and answer every possible question that a user of your design will encounter. Ideally you want the design to work, but functionality is extremely important. Being able to foresee problems with the functionality and knowing that the user/client will understand the design/interface without much thinking. If you continuously question and discover every possible facet of what you are creating… hopefully all questions will be discovered, discussed and analyzed to create a great design, great interaction with the user and a great experience that will be repeated if needed. One thing that is very important is bridging great design and great experience.