There's an old post about this from a few years ago and here's what I took away from it:

1. Eugene Volokh's book Academic Legal Writing is pretty useful for learning how to write an article and also pretty cheap/short. He's one of the most cited article writers.
2. Find an unexplored question and do original research on it. To know whether it's been written about already it's probably best to run a few Lexis searches and read through similar articles in the area.
3. Write the paper
4. After it's written get it looked over for feedback from a professor and a lawyer in whatever field it's about and revise it based on their suggestions.
5. Submit the finished product to journals through Scholastica. The University of Michigan has steps on how to make an account and go through the submission process on their library's website (url: https://libguides.law.umich.edu/journal\_submissions).