I started to create an article regarding CSS and HTML best practices. I personally believes everyone should know and understand theses practices and they are important when we code.
After some digging I found few articles that shows exactly what I am trying to explain here. So there they are:
CSS code can be very cumbersome and messy if you don't start the right way. Here's a good article about CSS you should know about before you start coding your CSS.
HTML is a mark-up language but should be treated as any other coding. Some code are good, some code are bad. Here's a good guide on what you need to do to build good good following the best practices.