[TheLem]

In my opinion it goes like this :

- Make a sketch of the design, form positioning or interface you want for a certain page.

- Try to translate this design to a more comprehensible form for your interpreter (I mean writing CSS lines).

- Long cycle of try and error, reading stackoverflow, testing, reading snippets.

Practice this for a certain amount of time (be patient!) you will find yourself a world class CSS "writer". The main basis is moving from a sketch to CSS script.

[mattj]

Similar experience, but I focused on finding UI elements I liked from native apps or websites and attempted to clone them without looking at the source, then played around with the result to figure out how I could simplify it, how it behaved cross browser, etc etc.

[Catalyst4NaN]

I really like the sound of this approach. It seems really simple but thanks for the tip!

[Moru]

And then restart the cycle next time your (or everyone elses) favourite browser does an update.