Some things the designer should do:
1) Formalize a color-palett, use the swatches menu and name the colors the same in your .less (or other) file.
Example: http://i.imgur.com/ILDyZfu.png
2) Use the layer comps menu, to reduce the clicking around.
And on your side, get the http://css3ps.com plugin to create css from layers, it's way better then the built in tool.
It's so easy now! There's even software that does the CSS for you (haven't tested myself but here's one free option), if you could put together a site with just HTML tags you already know more than you need to.
So much this.
There are also helpful plugins you can get for Photoshop that will tell you how to style something in accordance to the layer you have selected.
While these aren't necessarily great plugins for someone with lots of experience they definitely help get started on CSS. I came from a traditional graphic design background and this process /u/mrtemplates (just noticed the irony in his name and his suggestion) describes combined with a Photoshop CSS plugin helped me understand it quite a lot.
If you have access to photoshop, there is a plugin called css3ps that can help you transform layer styles to css. I haven't tried it yet but I've heard good things about it - might be worth a try.
sort of related, I used this Photoshop plugin once with success that converts layer properties/blend modes/etc into CSS3.
Like I said, only used it once so can't say it's consistently good but it's worth a shot.