What do you do well? Basketball, cooking, drawing, sewing, soccer? You didn't become really good without practice.
Consider your best academic area. Isn't this an area that you know something about--probably, quite a bit? You didn't learn how to read without first learning basics like recognizing letters and their sounds, hearing language spoken aloud, and learning basic vocabulary. New knowledge needs something to "stick" to, or else it has no context and the brain does not regard it as important. The more you know about something, the easier it is to learn more.
Here are some basic tips to employ this principle:
Before you read an assignment, preview it. Find out as much as you can before you read. Survey the title and headings. Study the pictures and charts. Read the summary. Familiarize yourself with the study questions. Think about what you already know about the subject. Try to recall what you already know. Then read the assignment.
Before you go to class, do all homework assignments and readings. The more you know about the subject, the easier it will be to take notes during the lecture.
Begin with basic level courses in the subject. Don't skip prerequisites.
Do extra research. Explore the internet. Create ways to experience the subject.