Add HTML and CSS Comments to Your Web Pages

Comment your web page markup and styles so that you have notes about what the section is doing and what your alternative choices are. Comments are also good to intentionally break/remove sections of your code without really getting rid of it.

[olafzijnbuis]

Nice video.
I often start with the comment. explaining what I like to achieve. Then fill out the code. And last, review the comments and extend or remove them.
Writing things out in pseudo-code really helps!