I have found in my time playing chess that more players worry about specific openings rather than applying the general principles of opening play to their game. This is mainly seen more with kids than with adults. However, even adults don't always follow the principles of opening player either. The biggest principle that is always missed seems to be the lack of development.
I have picked a recent online blitz game to showcase what a lag in development can do to your game. Then as true to this new format I have included my video as I go through the "Principles of Opening Play" using Chess.com's Lesson tool.
Here is the video on opening principles: