First get acquainted with the basics. Make sure that coding is fun and interesting. I recommend Codecademy for a free and fun introduction to programming.
If you prefer to blaze your own path, first decide on how frequently you want to build a site. Keep in mind that a greater frequency of building will result in more variety but less depth and vice versa.
Here is a great example of building a portfolio by creating weekly sites: How I finally learned to build stuff with Rails.
And here is inspiration in the form of learning by building daily sites: How to Get Inspired about Web Development.