Consider these your critical success factors or the KPI´s that every design should adhere to…
1. Simplicity: Less is more
KISS: Keep it simple, stupid! Get rid of the noise. Giving too many options confuses and scares away users. Let them explore and spark their curiosity! Minimise clutter, for example by combining function and communication in a single general-purpose element. Real success might be how quickly they get things done or even how much they spend NOT viewing your product/page..
2. Consistency and convention
Throughout your product, maintain the same styles (fonts, colors, sizes), positions (detail view is to the right of index) and terminology.
Convention refers to a common or standard way of solving a design problem. Some examples are typical GUI elements such as radio-buttons and checkboxes. Standard solutions save the user time by preventing them to become confused when identifying a designed element and learning how it works. Things that look different should act different. At times it is good to break conventions, but only when the new solution is truly more beneficial than the conventional solution.
User-centered design is paramount, but inevitably balancing these with business goals. Provide relevant, rich content and information. Ensure good information overview with minimal distraction or interuption.
5. Communication & Clarity
Provide the right feedback at the right moments. Clear structure and easy access to support. Errors, fast exits and undo.
Workload reduction. Support cognitive processes, don´t overload them. Improve user and system performance. Functional applications provide necessary tools for users to reach their goals quickly and effectively.
7. Emotional impact
Proper use of colours, fonts and layout. An appealing (attractive) and memorable user experience (viscal,). Young people are more brand sensitive, technical people like to surround themselves with more power. For more, see ‘Emotional design’ book.
Other than that, be sure to include: Performance (see Constraints blog post)
Also read my post about Laws of Interaction design.
Inspiration @ http://www.valcasey.com/webdesign/
See also my post User Experience heuristics
Consider human factors
and basics tricks http://ux.handson.co/