So the idea is to accumulate like a cumulative frequency. Put down the roots of programming and branch out with every new language while the trunk remains the same and strong!
So, you have three parts. Root, Branches and Trunk.
For the Roots part, I would suggest you to read this small ebook:
For the Branches part, developing a small application (might be a simple game) is a best way to know programming in and out. Be it of any purpose. It will strengthen your skills.
Now coming for the Trunk part, this will happen automatically if above both are done right!