Hi, this is my personal styleguide. I use it to share how I like to code. You can fork it on GitHub or ask me questions on Twitter.
A declaration block in CSS refers to an entire block of CSS between the < >brackets. For example:
.header  font-weight: bold; > 
A declaration refers to one property: value; line.
font-weight: bold; 
Here's some rules that focus on declaration blocks and lines.
.head
.head  display: block; border: 1px solid #a80; > 
Separate blocks of declarations by an empty line. Except for declarations that are single lines.
.col-1 < width: 50%; >.col-2
.col-1  width: 50%; > .col-2  width: 25%; > 
Every property within a rule set should be on it's own line. This helps with error detection when processing your CSS in a CI setup.
You can break the one line rule when a ruleset contains one declaration, it should be placed on a single line.
.call-to-action < width: 100px; height: 100px; >.email-link
.call-to-action  width: 100px; height: 100px; > .email-link  display: block; > .twitter-link  display: inline; > 
Whenever possible use the shorthand notation for properties rather than the full lines. For more reading I recommend this Mozilla article.
border-width: 1px; border-style: solid; border-color: #000; 
border: 1px solid #000; 
Find anything wrong with this guide? open an issue on GitHub.