Web development mistakes

A great article at Berea Street on some of the most common mistakes that experienced web professionals tend to make. A couple on this list really hit home with me which I will echo here:
(too much) Visual thinking
Treating the web as WYSIWYG – starting off by focusing on how things look instead of thinking about structure first, and presentation later.
Lack of semantics
Non-semantic markup. Basing the choice of which HTML element to use on the way most graphical browsers render it by default, instead of on which meaning the element has.
Read: Web development mistakes: 456 Berea Street