You are pointing a problem that most candidate are facing after a first round of preparation. Somehow you manage to sometime solve the case, but you haven't yet understood in details what make you succeed or not.
From now on, it is very important to identify each of the dimensions you need to improve, and on work it on individually.
1. Structure is the most common and impacting issue, since it will be very difficult to dive in the case if you don't cover the right topics or are not properly structured to do so. Forget about the pre-existing framework you can find in books. The one question you should keep in mind while building your structure is "Will each of the dimension of my approach bring insights to formulate a recommandation". I can provide with a very good exercice for this called structuring drills, contact me in pm if needed.
2. Drive and business sens come in second. You need to understand that you have the lead for the case resolution, and identifying insights from analysis you will conduct. So your attitude must be dynamic and always keep in mind that what you are looking for is insights not data.
3. Recommandation is not a conclusion ! Meaning that you are not closing the case by summarizing what you've just done. The first words you will prononce at this stage should directly answer to the question, and then bring the elements supporting this recommandation. Keep in mind, that in many cases this is not your recommandation itself that matter but the way you will structure your communication to deliver the message with a lasting impact.
I hope this help, don't hesitate to reach me if you need more details.