I would choose any known CMS and write plugins for it. Just look what others are doing and build it. You can make it also only for yourself.
Important is that you simply start and try out. If you have questions, you can fill Google with it. Stackoverflow is filled with solutions.
For example, you could write a review plugin for WordPress and rate websites on your blog. Or something similar. There are enough things you can do.
In any case: Just start!
PS: You can also simply help others and expand your skills.