I agree with @srg36 that the way to master the skill is a lot of practice and experience. I would like to add reading to that list. I took Technical Writing as an undergraduate course, I was good but not essential. Nobody was really in my field then and the teacher tried to generalized all students so they could only provide the structure but not correcting the sentences or content in even somewhat detailed. I learned a lot through writing myriads of lab reports in other Bio-based class. Reading lots of journals/news (especially the ones about your field) has been a great help in improving my technical vocabulary greatly. In many classes, you may have to summarize journal articles and present, I think it’s a great way to learn where you have only a certain amount of time to convey the info to the viewers in the most understandable way.