I, too, would like to become a better writer of English, and Time magazine would be a good standard for brevity and clarity.
However, my need to write better English is for legal work. I am currently doing legal research and document preparation for a pro se litigant for $300 a week. I love the work since I did pro se legal work for over 15 years as a maximum-security prisoner. See, e.g., Pratt v. Sumner, 807 F.2d 817 (9th Cir. 1987)(holding that a complaint against prison officials for blocking law books sent by professors of law was not legally frivolous). However, the difficulty of legal writing is that it often has to talk about convoluted and qualified legal principles and their application to facts, and it is very easy to end up with some very abstract mush.
In view of that, I am going to slowly work through a book about legal writing and legal reasoning by an author named Neumann. He made a very good point that even college writing skill often earns a good grade without demanding truly tight reasoning or real clarity. In other words, college writing often just goes through the organization and form of a thesis paper without demanding a tight and persuasive argument.
The following is a revised example of part of a brief that I wrote:
"Although she has been declared mentally incompetent in an unrelated action for guardianship and conservatorship brought by her son several months after her new marriage, case law apparently holds that a person can have sufficient mental competency to marry even if that person was placed under guardianship for lacking sufficient mental capacity to conduct business affairs."
That writing is heavy with a long-winded recital of qualified facts.
I think that learning to write legal work well, with the brevity and clarity of Time magazine articles, would be a hell of an achievement.