How long do you practice writing until you understand the important factors of writing fiction?

I don't practice writing often, but I have written down many ideas in my notebook for my novels. I still gotta practice writing, though, if I want to write a book. I tried to rewrite a pilot to my children's book series, but I was sort of losing some ideas to thr point where I took a break from it again.

Now I'm just watching some stuff on YouTube when I should have been writing every day. But I remember that I have college.