[stevoo]

Most of these are hard to measure. It will come down to your own variables.

Interviews are a whole different world so I don't think that they test how much you have actually improve.

Creating your own products is a great way to improve your code. Learn about the system your want to design, create the database, write your services, do the UI and iterate. After a few failed products you'll understand that what ever your wrote until know it was crap and your code will be cleaner and better.

The best would be to contribute to open source projects. That way you have to study other peoples code. Understand it. Improve it. And then send your code for it to be reviewed and merged for the whole world. Off course it will always depend on how good the original author of the project is.