I would recommend Python. It's easy to pick up and get going. No worries about frameworks, compilers, etc. Beyond that, C++ is pretty critical for most commercial applications. If Windows application development, I would say C#. For web development, PHP is probably the most useful. So you have some ideas. The best approach: find a project you want to work on and go. It's always good to have that motivation and you really do learn the most by doing.