How do I get good at studying?

I've never been good at studying, and even if I spend hours studying it's like I didn't study anything. I've always been like this, and I'm in my 30's now. I've always been just okay in school, but now I want to learn new skills and I want to be more efficient at studying. Any study tip is appreciated.<br><br>Edit: I changed the title to a more general question, and I'll be asking specific questions in the comments so that I can cover every front on this topic. Feel free to ask your own questions.