You got to be delighted to learn the basics from the Master. David has given us an article which sums up the Dex Basics while designing the UI. Read it here: Checklist for creating a new Dexterity Window.
I would add one more point to this: When you compile your code and see some Warnings, just be a bit patient and go thru’ each Warning. You would certainly be looking at something really critical which may not pose critical at the time of compiling. Take a look at this article of mine for instance: Declaring Variables to Relevant Datatypes. This could have been avoided if that Developer had taken care of the Warning message Possible Data Loss due to Type Mismatch.
While Dex Basics have been taught again and again, articles like this are still needed as we tend to forget the basics while concentrating on the complexities. For a Customer UI is the window to a Product. He/She does not really worry about what is written beneath that UI and how it is.
A product is judged first by it’s Look & Feel and only then the Features itself. I am sure many would disagree but that’s my humble thought.