How can I improve my writing skills?

I learned how to write from my dad and my brother.

Here are a few GUIDELINES to improve your writing skills:
Improve your writing by reading good writers.
Improve your writing by practicing every day.
Improve your writing by editing a day later.
Improve your writing by establishing a structure.
Improve your writing by finding your “voice”.
Improve your writing by understanding that factual, listed content is powerful.
Adverbs, prepositional phrases, and “est” are out.
Use the right tone. Mine is straight forward, succinct.
Select a “voice of author”. Mine is authoritative.
Use the power of authority in pronouns: first person singular, second person, third person.
Grammar (OK sometimes). For me, it’s write like you speak.
Research vs. your knowledge. Proof vs. opinion. I use knowledge and opinion.
Use graphic and alliterative word choices like “vomit” and “puke”.
Keep paragraphs short.
Use repeated themes. I use: MAJOR CLUE, or “Think about this…”
Use bold and CAPS to make points, and emphasize words.
Grab me at the beginning. Start with a question or short statement.
Give me meat in the middle. All meat.
Make me smile, think, or act at the end. End with impact.

BIG SECRET: Read aloud when you edit. How does it sound, not how does it read.

ASK YOURSELF THIS: Where’s the impact? Where’s the meat? Where’s the point? Where’s the hook? Is it compelling?
Will the reader want to read it all? Will the reader think as a result of this writing? Will the reader act as a result of this writing?

MAJOR CLUE: When is the last time you wrote an article in a publication that your customers and prospects read?
The answer to that question is most likely, “never”.
Wouldn’t it be cool if you walked in on a sales call and saw the magazine you wrote in — open to the page where your article appears — on the desk of your probable purchaser?
Writing is a key differentiator. I’ve used for 14 years. Writing will not just lead to differentiation. Writing is the credibility you need to buy buyer confidence.

Source: Little Red Book of Sales Answers, Jeffrey Gitomer, p. 16-17