User interface is a big subject, and a comprehensive view is well beyond the scope of this book. There are many books on the subject alone. For our purposes, I wish to provide you with some ideas and inspiration. With that in mind, this is a list of best practices:

• Clarity: This is one that hits all the lists. A clear and easily understood interface will have them in and out in no time. The user remembers whether an experience was good or bad, though likely not on a conscious level. This can have a direct effect on whether or not a user wishes to return to that interface.
• Be forgiving /flexible: The more natural a user interface is, the less likely the user is to actually read what the controls say. As a result, people will make mistakes, even with the best design. Ensure that you are prepared for the user to make these mistakes and fix them when they do happen.
• Keep it simple: As mentioned previously, an interface that is barely noticeable wins, hands down.
• Keep it familiar: As developers, our purpose is to find solutions to fix problems. Often, the problem we are finding a solution for has already been solved. When this is the case, why would we not use one of the solutions that exist? To learn is a fair answer, but you don't want to reinvent the button or input field, neither does your user want to relearn an entire interface when a common solution would suffice perfectly well.
• Consistency: Use similar elements for similar functions throughout your application. Inputs that look similar should also behave in a similar way.