First, there are 2 types of prep, General Prep and Substantive Prep.
General Prep consist of things like learning how to brief cases, learning the basics of issue spotting, learning the process of outlining (and how best to outline specifically in relation to law school exams), learning how to read opinions (or getting used to reading opinions), or any law school exam test taking prep/studying tips. The idea of general prep is working to build a really great foundation that you can further build on throughout the semester. It should help you structure your studying from the very beginning, as well as give you a good idea of what you should be focusing on during class and as you read cases. It should also give you tools and tips to make “thinking like a lawyer” and legal analysis come easier. Additionally my version of general prep will help me begin the basics of learning how to write like a lawyer.
Substantive prep is actually getting into the law and beginning to learn the basics of all the classes (or the hardest classes) 1Ls typically take (such as torts, property, or constitutional law). Some people do this by reading Explanations & Examples (E&Es) books or Hornbooks (which are somewhat like the law school version of “sparknotes”) on these different subjects. The idea of substantive prep is that you try to grasp some of the basic legal concepts before you officially start school, which could make class easier to understand and take away some of the learning curve to also contribute to structuring your studying and helping you understand cases and hypotheticals better.
My focus is going to be on general prep because I personally don’t think substantive prep is necessary or significantly helpful.