I write general styles like definitions for *, a, p, ul etc first and after that I put everithing in DOM order when possible. Starting at the startpage of the website/project.
Within the selectordefinitions I write general definitions like width, heigt, displaytype and position (top/left.. margin, padding) first. Then contentspecific definitions like fontdefinitions. At the end I write border and background definitions.
That way it's an ease to see if an element hast a specific definitions, because I know if I'm looking for the width and the first definition is not the with then there is no width set for this element.