How do I improve my BJJ defense overall?

The best way to improve defense is to practice it intentionally. Instead of always starting from a neutral position, ask to start in mount bottom or side control bottom during rolling. This forces you to work your escapes under live resistance. Study the common submission attacks from each position and learn where the danger points are. If you know that the armbar from mount starts with your opponent isolating your arm, you can focus on keeping your elbows connected to your body. Defensive BJJ is about recognizing threats early. A submission is much easier to defend in its setup phase than once it is fully locked in. Pay attention to your opponent grips and body position because these telegraph their intentions. Off the mat, watch instructionals focused on escapes and defense. Many top competitors have excellent defensive instructional content that teaches systematic approaches to escaping every bad position.