How do you combine learning new technologies with practicing what you already know?

Generally, what I already know well enough to feel comfortable I use at work and so I have a lot of practice already. Despite that I often read documentation and books of what I already use at work to improve my skills. For new technologies I generally come up with some project to practice, a bit per day. I think I find a good equilibrium that way.

By making new features/projects? how else.

For learning side-projects I saw that about a proportion of 50/50 is ok, if you add more unknown stuff you will get more frustrated because nothing works.

In a payed/professional environment the ratio is of course a lot smaller, with a 10% I would add feature flags, A/B tests or other techniques to limit and test the "new".

I evaluate new technologies by whether they will further or hinder my research. These are new (to me): MVC, Javascript, Jquery help my research. Entity Framework hinders my research.

I write lots of new stuff in the new technologies that help my research.

I rewrite code using the technologies that hinder my research to use technologies that further my research. So I rewrite Entity Framework code into ADO because ADO is not an obstacle and Entity Framework is.

Either way I learn something about both kinds of technologies.