It's become increasingly rare to see web page addresses with a file extension, such as ".html". It's a good idea to clean these up, and it's easy to do.
The performance of your site – the speed with which it loads and responds to user actions – is crucial to its success. There's a lot you can do to improve this.
The SASS preprocessor promises to take much of the grunt work out of developing CSS. Lengthy, repetitive spriting code would especially benefit from this.