1) Start with the latest versions.
With any technology, there is no reason to start with the version that was popular 5 years ago. Start learning with what is current. As of this writing, HTML5 and CSS3 are the standards. Begin here and work your way forward. You will actually get to avoid a lot of the issues inherent in previous versions.
2) Create a simple WordPress site and then dissect it.
You want me to create a site before I know who to actually build it? Yes. This is how I learned. I installed WordPress and created a simple site. Do not worry, there are plenty of resources around to help you do this. Once installed and the website is up and running, dissect it piece by piece. Figure out what goes into the header tag. Learn about meta tags. View the page source of the home page and begin to understand DIVs. Learn how the navigation structure works, etc. There is no better tutor than real practice. If you have a real site to play with, it makes it all the more exciting. You will eventually learn your craft and gain proficiency.
3) Work top to bottom.
Start with the header tag and then the body tag. Then begin to fill in the gaps. Start at the top working on logo placement and navigational structure. The latter will keep you busy for a while! Move to understanding body layout: two column and three column design. Understand sidebars. Finally, work on footers. Then go back and fill in some of the meat. Figure out image placement and link colorization. Understand text arrangement: paragraphs, ordered and unordered lists, blockquotes, etc.
4) Find excellent tutorials
There are plenty of good tutorials around. A few words of advice: Start with a free tutorials but move on quickly to solid "pay" resources whether that is a book or a website. A lot of tutorial websites have a reputation. Search their names in Google to see if there are any reviews. A lot of tutorials are not updated to the latest version of the technology. So be careful! Double check and make sure you are working with HTML5 and CSS3 material.
5) Use the Internet everyday
Chances are you would not be interested in learning HTML and CSS if you were not already an avid web user. Continue to use the web everyday. Visit all kinds of sites. View their page source and learn how they structure their site. Appreciate good design from bad design.
Lastly, my bonus tip, have fun!