Use a Reset Stylesheet
This is one frequently mentioned as a CSS best practice. The goal of a reset stylesheet is to reduce inconsistencies among browsers by explicitly setting styles to most of the HTML elements. This ensures that things like font sizes and line heights all render the same on different browsers. Also, the reset clears the default paddings/margins that some browsers have.
Not only does having a reset stylesheet account for browser inconsistencies, it’s good to use them to give each site a known foundation when coding. Keeping the foundation the same for all sites will speed along the development.