Wiki on actual things you can do/read?

[jtagcat]

Caching. I have minimal idea on how it works.

Is a CSS file for only the things needed on each page or a common CSS file better? Does the CSS file get downloaded every time?

[KeenRivals]

A very brief overview is that when the server sends a file it can include an Expires and/or Cache-Control header, which tells the browser when it needs to refresh that content. Until that time passes, the browser can choose to use the cached copy of the file. At BMFW I use Apache's mod_expires to set a +1 week expiration on the content via .htaccess.

The nuts and bolts of it is usually you want to provide a separate CSS file and let browsers cache that. Some people argue that in-lining your important CSS in your pages helps browsers do initial rendering faster since it doesn't have to do an extra fetch. My response to that is if web pages weren't obscenely large to begin with the paint issues would be totally negligible. But, I'll admit that over poor network connections, extra fetches can perform badly. I prefer to keep it very simple and just keep the CSS separate. IMO the best way to help people with bad connections is to keep page + resource weight as small as possible.