This method is "The Power of Reading" and it comes from an article by Dr.Stephen Krashen. He is probably the number one expert on language learning and language teaching in the world.
Here're some questions:
1.How do people ,native speakers, and people learning foreign languages learn vocabulary?
2.How do they get good grammar?
3.How do they get excellent writing skills?
The answer is : one of the most important methods is reading.
Reading,it means reading a lot of easy books, we learn to read, grammar and writing skills by reading . For example, you find a new word when you're reading a veryeasy book, you know the general meaning ,so you can guess the meaning of the new word, so you don't have to memorize it. Then you recognize it in another paragraph, later in different books. Then you will know it forever without learning it on purpose. This is the correct way to learn vocabulary. By the way, when you read ,remember toread for fun !
It's same for grammer and writing skills.
In thi sway, we can continue to improve in our second language without classes, without teachers ,without study. Do it and you'll find your subconsciously acquired good writing styles .