Well said. The #1 rule I used to follow is I am on this control what can I do here and is it clear. The #2 rule is What is my next step from step #1 and

Well said. The #1 rule I used to follow is I am on this control what can I do here and is it clear. The #2 rule is What is my next step from step #1 and is it easy to find where I currently am. Break either of those and the GUI will be confusing. Disappearing controls makes you think something is wrong. I would typically go with disabled and a clear indicator of the something else needing to be filled out. If that was not achievable a tooltip on the disabled control to tell the user what to do. The way to achieve it is to pretend you are on 2 hours of sleep and not very computer savvy. Now you can go too far and make the whole thing a busy mess and then it is unclear where to even begin. A good rule of thumb with that is left to right top to bottom, keep scrolling to a minimum. Most people get that. One I was using just yesterday was jumping around in the page and the 'finish' control was in the top left and scrolled off the page.