Order of tags in <head></head>
Solution 1:
Optimization
According to the folks over at Yahoo! you should put CSS at the top and scripts at the bottom because scripts block parallel downloads. But that is mostly a matter of optimization and is not critical for the page actually working. Joeri Sebrechts pointed out that Cuzillion is a great way to test this and see the speed improvement for yourself.
Multiple Stylesheets
If you are linking multiple stylesheets, the order they are linked may affect how your pages are styled depending on the specificity of your selectors. In other words, if you have two stylesheets that define the same selector in two different ways, the latter will take precedence. For example:
Stylesheet 1:
h1 { color: #f00; }
Stylesheet 2:
h1 { color: #00f; }
In this example, h1 elements will have the color #00f because it was defined last with the same specificity:
Multiple Scripts
If you are using multiple scripts, the order they are used may be important if one of the scripts depends on something in another script. In this case, if the scripts are linked in the wrong order, some of your scripts may throw errors or not work as expected. This, however, is highly dependent on what scripts you are using.
Solution 2:
The accepted answer is kind of wrong, depending on the encoding of the document. If no encoding is sent by in the HTTP header, the browser has to determine the encoding from the document itself.
If the document uses a <meta http-equiv="Content-Type" … declaration to declare its encoding, then any ASCII-valued character (character code < 128) occurring before this statement must be an ASCII value, as per HTML 4 spec. Therefore, it's important that this meta declaration occurs before any other element that may contain non-ASCII characters.
Solution 3:
It's recommended to put the meta tag with the character encoding as high as possible. If the encoding is not included in (or differs from) the response header of the requested page, the browser will have to guess what the encoding is. Only when it finds this meta tag it knows what it is dealing with and it will have to read everything it has already parsed again.
See for instance Methods for indicating the character set.
Solution 4:
One important thing to note: if you're using the Internet Explorer meta X-UA-Compatible tag to switch rendering modes for IE, it needs to be the first thing in the HEAD:
<head> <meta http-equiv="X-UA-Compatible" content="IE=7" /> <title>Page title</title> ...etc </head>