How can programming skills be improved?
The only way to learn a lot of things, maybe most things, is practice and feedback. In a standard course (not online), the professor assigns some work to do - homework, projects, .... The professor then gives you feedback on it - grades, but hopefully more. 

To learn on your own, you want to try to simulate this as much as you can. So, to learn something, you not only have to see and hear about it, or even read about it, you have to do it. Moreover, you need some way to get feedback on the success of your efforts. 

If the videos don't suggest projects then you will have to find them elsewhere, perhaps in a textbook. Do a lot of small and large projects. 

But then the feedback part is just as important. One possible way to simulate that is to work with a friend in your learning. Each of you does the same exercise separately and then exchange your work and each comment on and improve the other's work. This isn't perfect, since the other person isn't an expert, but it is better than nothing. 

You might even be able to use an online forum to get comments on your attempts. The Code Review here, might work for you, though I don't know how welcoming they are of novices.  Be sure to see their "help center" for guidance.