Simple: Wait until your LRW Professor TELLS you how they want you to write.
If you aren't in school yet, then don't waste your time learning bad habits that will have to be UNLEARNED once you get in school. Two Law Professors at the same school will require different things from their students during the course of the semester.
I disagree some things will remain the same across LWR programs, mainly grammar, style, punctuation, capitalization, when to use the serial comma etc. Hence the recommendation of a style book. During your LRW class is not the time to brush up on your basic grammar rules, do that over the summer. Also I think LRW at least to style (avoid passive voice, short over long words, not using the same words over and over again) and construction (start with your best point, bury bad points in the middle etc.) which again, remain the same across classes, is one of the easiest things in law school to improve on, if you have the time, which one won’t once LRW actually starts.
If you are in law school and you DON'T know that it is improper to end a sentence with a prepositional phrase then you don't need any legal books. You need Hooked on Phonics or something of that remedial nature.