CSS and Stylevars: How should I style my themes?

[josh_krz]

I am starting to design a new theme for my forum. I have done it before but in a very sloppy manner.

I want to create the theme entirely from scratch however I am confused as to how I should style objects.

Before I just added all my CSS into additional.css and prefixed my classes so they do not clash with the other CSS. I feel this is a sloppy way of designing because there is still loads of left over CSS from vBulletin.

I have tried manually changing the vBulletin CSS but it reverts back after certain actions such as updating forums.

So what I am asking is how do you design templates for your forums and what are the best practices when doing so?

Thank you!