Considerable, well-funded research. Try to separate functional decisions from UI decisions. Develop the optimal number of features. Each additional features adds another level of complexity. Never ask users HOW to do it.
Users are poor designers, good refiners.
Stay away from 1st time users. Do not design for 1st time users unless that is your primary audience. Don't test using 1st time users. Interfaces need to capture the attention of 1st time users and satisfy them when they come back. User Preferences Asking users if they like a site is NOT a good indication of the site's overall usability.